[libromdata] Remove PartitionFile in a few cases where it isn't needed.

In these cases, a PartitionFile was created that started at offset 0
and had the size of the entire IDiscReader.

This was used solely to allow using an IDiscReader as an IRpFile.
Since IDiscReader is now derived from IRpFile, this isn't necessary.
Removing PartitionFile in these cases reduces code size a bit, as
well as reducing runtime overhead.

Code size difference: (64-bit Gentoo Linux, gcc-13.2.0, release build, no LTO)

   text    data     bss     dec     hex filename
2049515   70792     704 2121011  205d33 libromdata.so.4 [before]
2048911   70760     704 2120375  205ab7 libromdata.so.4 [after]
   -604     -32       0    -636    -27c Difference

src/libromdata/Console/Dreamcast.cpp

@@ -772,11 +772,7 @@ int Dreamcast::loadFieldData(void)
 		isoData = d->gdiReader->openIsoRomData(3);
 	} else {
 		// ISO object for ISO-9660 PVD
-		PartitionFilePtr isoFile = std::make_shared<PartitionFile>(
-			d->discReader.get(), 0, d->discReader->size());
-		if (isoFile->isOpen()) {
-			isoData = std::make_shared<ISO>(isoFile);
-		}
+		isoData = std::make_shared<ISO>(d->discReader);
 	}
 
 	if (isoData && isoData->isOpen()) {

src/libromdata/Console/Xbox360_XEX.cpp

@@ -1188,18 +1188,21 @@ const EXE *Xbox360_XEX_Private::initEXE(void)
 	// PE section, so we don't have to look anything up.
 
 	// Attempt to open the EXE section.
-	// Assuming a maximum of 8 KB for the PE headers.
-	IRpFilePtr peFile_tmp;
 #ifdef ENABLE_LIBMSPACK
 	if (!lzx_peHeader.empty()) {
-		peFile_tmp = std::make_shared<MemFile>(lzx_peHeader.data(), lzx_peHeader.size());
+		IRpFilePtr peFile_tmp = std::make_shared<MemFile>(lzx_peHeader.data(), lzx_peHeader.size());
+		if (peFile_tmp->isOpen()) {
+			EXE *const pe_exe_tmp = new EXE(peFile_tmp);
+			if (pe_exe_tmp->isOpen()) {
+				pe_exe = pe_exe_tmp;
+			} else {
+				delete pe_exe_tmp;
+			}
+		}
 	} else
 #endif /* ENABLE_LIBMSPACK */
 	{
-		peFile_tmp = std::make_shared<PartitionFile>(peReader.get(), 0, PE_HEADER_SIZE);
-	}
-	if (peFile_tmp->isOpen()) {
-		EXE *const pe_exe_tmp = new EXE(peFile_tmp);
+		EXE *const pe_exe_tmp = new EXE(peReader);
 		if (pe_exe_tmp->isOpen()) {
 			pe_exe = pe_exe_tmp;
 		} else {

src/libromdata/Handheld/Nintendo3DS.cpp

@@ -595,8 +595,6 @@ int Nintendo3DSPrivate::openSRL(void)
 	}
 
 	// Attempt to open the SRL as if it's a new file.
-	// TODO: IRpFile implementation with offset/length, so we don't
-	// have to use both DiscReader and PartitionFile.
 
 	// Check if this content is encrypted.
 	// If it is, we'll need to create a CIAReader.
@@ -615,15 +613,8 @@ int Nintendo3DSPrivate::openSRL(void)
 		return -EIO;
 	}
 
-	// TODO: Make IDiscReader derive from IRpFile.
-	// May need to add reference counting to IRpFile...
-	RomDataPtr srlData;
-	PartitionFilePtr srlFile = std::make_shared<PartitionFile>(srlReader.get(), 0, length);
-	if (srlFile->isOpen()) {
-		// Create the NintendoDS object.
-		srlData = std::make_shared<NintendoDS>(srlFile, true);
-	}
-
+	// Create the NintendoDS object.
+	RomDataPtr srlData = std::make_shared<NintendoDS>(srlReader, true);
 	if (srlData && srlData->isOpen() && srlData->isValid()) {
 		// SRL opened successfully.
 		this->mainContent = std::move(srlData);

src/libromdata/Handheld/PSP.cpp

@@ -551,9 +551,7 @@ int PSP::loadFieldData(void)
 	// TODO: Parse firmware update PARAM.SFO and EBOOT.BIN?
 
 	// ISO object for ISO-9660 PVD
-	// TODO: DiscReader overload for ISO.
-	const PartitionFilePtr ptFile = std::make_shared<PartitionFile>(d->discReader.get(), 0, d->discReader->size());
-	ISO *const isoData = new ISO(ptFile);
+	ISO *const isoData = new ISO(d->discReader);
 	if (isoData->isOpen()) {
 		// Add the fields.
 		const RomFields *const isoFields = isoData->fields();