Release all keyboard keys on focus loss (fixes #1987)

src/frontend/qt_sdl/Input.cpp

@@ -128,6 +128,11 @@ void KeyRelease(QKeyEvent* event)
             KeyHotkeyMask &= ~(1<<i);
 }
 
+void KeyReleaseAll()
+{
+    KeyInputMask = 0xFFF;
+    KeyHotkeyMask = 0;
+}
 
 bool JoystickButtonDown(int val)
 {

src/frontend/qt_sdl/Input.h

@@ -40,6 +40,7 @@ void CloseJoystick();
 
 void KeyPress(QKeyEvent* event);
 void KeyRelease(QKeyEvent* event);
+void KeyReleaseAll();
 
 void Process();
 

src/frontend/qt_sdl/Window.cpp

@@ -916,6 +916,7 @@ void MainWindow::onAppStateChanged(Qt::ApplicationState state)
 {
     if (state == Qt::ApplicationInactive)
     {
+        Input::KeyReleaseAll();
         if (Config::PauseLostFocus && emuThread->emuIsRunning())
             emuThread->emuPause();
     }