UI: Check to ensure window starts up inside a monitor

Fixes an issue where the main window would load off-screen if its last
saved position was inside a monitor that no longer exists.

obs/window-basic-main.cpp

@@ -132,6 +132,9 @@ OBSBasic::OBSBasic(QWidget *parent)
 		int posy = config_get_int(App()->GlobalConfig(), "BasicWindow",
 				"posy");
 
+		if (!WindowPositionValid(posx, posy))
+			posx = posy = 0;
+
 		setGeometry(posx, posy, width, height);
 	}