Qt: Disable attempted linking betwen incompatible platforms (fixes #2702)

CHANGES

@@ -18,6 +18,7 @@ Other fixes:
  - Qt: Disable sync while running scripts from main thread (fixes mgba.io/i/2738)
  - Qt: Fix savestate preview sizes with different scales (fixes mgba.io/i/2560)
  - Qt: Properly cap number of attached players by platform (fixes mgba.io/i/2807)
+ - Qt: Disable attempted linking betwen incompatible platforms (fixes mgba.io/i/2702)
 Misc:
  - GB Serialize: Add missing savestate support for MBC6 and NT (newer)
  - GBA: Improve detection of valid ELF ROMs

src/platform/qt/MultiplayerController.cpp

@@ -229,6 +229,9 @@ bool MultiplayerController::attachGame(CoreController* controller) {
 		default:
 			return false;
 		}
+		m_platform = controller->platform();
+	} else if (controller->platform() != m_platform) {
+		return false;
 	}
 
 	mCoreThread* thread = controller->thread();

src/platform/qt/MultiplayerController.h

@@ -9,6 +9,7 @@
 #include <QMutex>
 #include <QObject>
 
+#include <mgba/core/core.h>
 #include <mgba/core/lockstep.h>
 #ifdef M_CORE_GBA
 #include <mgba/internal/gba/sio/lockstep.h>
@@ -77,6 +78,8 @@ private:
 		GBASIOLockstep m_gbaLockstep;
 #endif
 	};
+
+	mPlatform m_platform = mPLATFORM_NONE;
 	QList<Player> m_players;
 	QMutex m_lock;
 };