sdlwindow.cpp: close m_thread w/o std::terminate being called

src/Backends/SDLBackend.cpp

@@ -55,6 +55,7 @@ namespace gamescope
 		GAMESCOPE_SDL_EVENT_CURSOR,
 
 		GAMESCOPE_SDL_EVENT_COUNT,
+		GAMESCOPE_SDL_EVENT_REQ_EXIT,
 	};
 
 	class CSDLConnector final : public IBackendConnector
@@ -113,6 +114,7 @@ namespace gamescope
 	{
 	public:
 		CSDLBackend();
+		~CSDLBackend();
 
 		/////////////
 		// IBackend
@@ -515,6 +517,11 @@ namespace gamescope
 		// Do nothing.
 	}
 
+	CSDLBackend::~CSDLBackend() {
+		PushUserEvent(GAMESCOPE_SDL_EVENT_REQ_EXIT);
+		m_SDLThread.join();
+	}
+
 	void CSDLBackend::SDLThreadFunc()
 	{
 		pthread_setname_np( pthread_self(), "gamescope-sdl" );
@@ -912,6 +919,9 @@ namespace gamescope
 
 						SDL_SetCursor( m_pCursor );
 					}
+					else if ( event.type == GetUserEventIndex( GAMESCOPE_SDL_EVENT_REQ_EXIT ) ) {
+						return;
+					}
 				}
 				break;
 			}