UI: Use rect intersection test for validating position

Instead of checking to see if the window's position is valid, check to
see if the rectangles of the window and the monitor intersect via a
rectangle intersection test.

UI/window-basic-main.cpp

@@ -137,9 +137,7 @@ OBSBasic::OBSBasic(QWidget *parent)
 		restoreGeometry(byteArray);
 
 		QRect windowGeometry = normalGeometry();
-		int posx = windowGeometry.x();
-		int posy = windowGeometry.y();
-		if (!WindowPositionValid(posx, posy)) {
+		if (!WindowPositionValid(windowGeometry)) {
 			QRect rect = App()->desktop()->availableGeometry();
 			setGeometry(QStyle::alignedRect(
 						Qt::LeftToRight,