Fallback on printing invalid wide string

In case the string to be printed contains invalid wide characters, fall
back to print as ASCII string.

Closes: htop-dev#1373

RichString.c

@@ -66,17 +66,19 @@ static inline int RichString_writeFromAscii(RichString* this, int attrs, const c
 
 static inline int RichString_writeFromWide(RichString* this, int attrs, const char* data_c, int from, int len) {
    wchar_t data[len + 1];
-   len = mbstowcs(data, data_c, len);
-   if (len <= 0)
+   size_t ret = mbstowcs(data, data_c, len);
+   if (ret == 0)
       return 0;
+   if (ret == (size_t)-1)
+      return RichString_writeFromAscii(this, attrs, data_c, from, len);
 
-   int newLen = from + len;
+   int newLen = from + ret;
    RichString_setLen(this, newLen);
    for (int i = from, j = 0; i < newLen; i++, j++) {
       this->chptr[i] = (CharType) { .attr = attrs & 0xffffff, .chars = { (iswprint(data[j]) ? data[j] : L'\xFFFD') } };
    }
 
-   return len;
+   return ret;
 }
 
 int RichString_appendnWideColumns(RichString* this, int attrs, const char* data_c, int len, int* columns) {