Qt: Fix e-Reader scanning function reentry (fixes #2693)

CHANGES

@@ -5,6 +5,7 @@ Features:
 Other fixes:
  - Qt: Manually split filename to avoid overzealous splitting (fixes mgba.io/i/2681)
  - Qt: Expand criteria for tag branch names (fixes mgba.io/i/2679)
+ - Qt: Fix scanning specific e-Reader dotcodes (fixes mgba.io/i/2693)
  - Res: Fix species name location in Ruby/Sapphire revs 1/2 (fixes mgba.io/i/2685)
 Misc:
  - GB Serialize: Add missing savestate support for MBC6 and NT (newer)

src/platform/qt/CoreController.cpp

@@ -914,7 +914,10 @@ void CoreController::scanCard(const QString& path) {
 		if (!file.open(QIODevice::ReadOnly)) {
 			return;
 		}
-		m_eReaderData = file.read(2912);
+		QByteArray eReaderData = file.read(2912);
+		if (eReaderData.isEmpty()) {
+			return;
+		}
 
 		file.seek(0);
 		QStringList lines;
@@ -936,6 +939,7 @@ void CoreController::scanCard(const QString& path) {
 			}
 		}
 		scanCards(lines);
+		m_eReaderData = eReaderData;
 	} else if (image.size() == QSize(989, 44) || image.size() == QSize(639, 44)) {
 		const uchar* bits = image.constBits();
 		size_t size;