fix: swaps quote nan to bnjs (#9848)

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## **Description**

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This PR fixes an issue where the app crashes after fetching a Swaps
quote. This is caused by `renderFromWei(missingEthBalance)` when
`missingEthBalance` is `"NaN"`.

The root issue is that
`accountTrackerControllerState.accounts[addr].balance` flip flops
between `undefined` and a string hex value. Swaps checks the gas token
balance to make sure the user has enough to submit the Swap transaction.
This PR does not solve that issue, it only adds guards to prevent the
app from crashing.

## **Related issues**

Fixes: #9672

## **Manual testing steps**

1. Go to Swaps
2. Fetch a quote
3. Sit on quote view screen and wait. This might take some time. If you
throttle your network, it seems to happen more often.
4. It should not crash the app

## **Screenshots/Recordings**

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before and after of your change. -->
n/a

### **Before**

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### **After**

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## **Pre-merge author checklist**

- [x] I’ve followed [MetaMask Coding
Standards](https://github.com/MetaMask/metamask-mobile/blob/main/.github/guidelines/CODING_GUIDELINES.md).
- [x] I've completed the PR template to the best of my ability
- [x] I’ve included tests if applicable
- [ ] I’ve documented my code using [JSDoc](https://jsdoc.app/) format
if applicable
- [x] I’ve applied the right labels on the PR (see [labeling
guidelines](https://github.com/MetaMask/metamask-mobile/blob/main/.github/guidelines/LABELING_GUIDELINES.md)).
Not required for external contributors.

## **Pre-merge reviewer checklist**

- [ ] I've manually tested the PR (e.g. pull and build branch, run the
app, test code being changed).
- [ ] I confirm that this PR addresses all acceptance criteria described
in the ticket it closes and includes the necessary testing evidence such
as recordings and or screenshots.

app/components/UI/Swaps/QuotesView.js

@@ -586,6 +586,9 @@ function SwapsQuotesView({
     const ethAmountBN = isSwapsNativeAsset(sourceToken)
       ? sourceBN
       : new BigNumber(0);
+
+    // accounts[selectedAddress].balance might be undefined
+    // BigNumber(undefined) returns "NaN", which causes missingEthBalance to be "NaN" downstream
     const ethBalanceBN = new BigNumber(accounts[selectedAddress].balance);
     const gasBN = toWei(selectedQuoteValue?.maxEthFee || '0');
     const hasEnoughEthBalance = ethBalanceBN.gte(ethAmountBN.plus(gasBN));
@@ -1674,6 +1677,12 @@ function SwapsQuotesView({
     hasEnoughTokenBalance &&
     hasEnoughEthBalance;
 
+  const shouldShowNeedMoreAlert =
+    (!isSwapsNativeAsset(sourceToken) && !hasEnoughTokenBalance) ||
+    (isSwapsNativeAsset(sourceToken) &&
+      !hasEnoughEthBalance &&
+      missingEthBalance?.isNaN() === false);
+
   return (
     <ScreenView
       contentContainerStyle={styles.screen}
@@ -1682,7 +1691,7 @@ function SwapsQuotesView({
       scrollEnabled={!isSwiping}
     >
       <View style={styles.topBar}>
-        {(!hasEnoughTokenBalance || !hasEnoughEthBalance) && (
+        {shouldShowNeedMoreAlert && (
           <View style={styles.alertBar}>
             <Alert small type={AlertType.Info}>
               {`${strings('swaps.you_need')} `}

app/util/number/index.js

@@ -312,17 +312,22 @@ export function fiatNumberToTokenMinimalUnit(
 export function renderFromWei(value, decimalsToShow = 5) {
   let renderWei = '0';
   // avoid undefined
-  if (value) {
-    const wei = fromWei(value);
-    const weiNumber = parseFloat(wei);
-    if (weiNumber < 0.00001 && weiNumber > 0) {
-      renderWei = '< 0.00001';
-    } else {
-      const base = Math.pow(10, decimalsToShow);
-      renderWei = (Math.round(weiNumber * base) / base).toString();
+  // This function can throw an error if value is "NaN", so wrap in try/catch
+  try {
+    if (value) {
+      const wei = fromWei(value);
+      const weiNumber = parseFloat(wei);
+      if (weiNumber < 0.00001 && weiNumber > 0) {
+        renderWei = '< 0.00001';
+      } else {
+        const base = Math.pow(10, decimalsToShow);
+        renderWei = (Math.round(weiNumber * base) / base).toString();
+      }
     }
+    return renderWei;
+  } catch (e) {
+    return renderWei;
   }
-  return renderWei;
 }
 
 /**

app/util/number/index.test.ts

@@ -403,6 +403,10 @@ describe('Number utils :: renderFromWei', () => {
     expect(renderFromWei('133700000000000000')).toEqual('0.1337');
     expect(renderFromWei('1337')).toEqual('< 0.00001');
     expect(renderFromWei('0')).toEqual('0');
+
+    // https://github.com/MetaMask/metamask-mobile/issues/9672
+    // fromWei will throw error if "NaN" is passed
+    expect(renderFromWei('NaN')).toEqual('0');
   });
 
   it('renderFromWei using BN number', () => {