Qt: Cap the maximum number of multiplayer windows

CHANGES

@@ -31,6 +31,7 @@ Bugfixes:
  - Qt: Better cleanup when a game crashes
  - Qt: Fix open ROM dialog filtering for archive formats
  - ARM7: Fix Thumb MUL timing
+ - Qt: Cap the maximum number of multiplayer windows
 Misc:
  - Qt: Handle saving input settings better
  - Debugger: Free watchpoints in addition to breakpoints

src/platform/qt/GBAApp.cpp

@@ -67,7 +67,10 @@ bool GBAApp::event(QEvent* event) {
 	return QApplication::event(event);
 }
 
-Window* GBAApp::newWindowInternal() {
+Window* GBAApp::newWindow() {
+	if (m_multiplayer.attached() >= MAX_GBAS) {
+		return nullptr;
+	}
 	Window* w = new Window(&m_configController, m_multiplayer.attached());
 	m_windows[m_multiplayer.attached()] = w;
 	w->setAttribute(Qt::WA_DeleteOnClose);