UI: Fix multiview hang

This could cause an infinite recursion if "show_in_multiview" was false
for a scene.

Closes obsproject/obs-studio#1426

UI/window-projector.cpp

@@ -927,8 +927,9 @@ void OBSProjector::UpdateMultiview()
 	siScaleY  = (scenesCY - thicknessx2) / fh;
 
 	numSrcs = 0;
-	while (numSrcs < scenes.sources.num && numSrcs < maxSrcs) {
-		obs_source_t *src = scenes.sources.array[numSrcs];
+	size_t i = 0;
+	while (i < scenes.sources.num && numSrcs < maxSrcs) {
+		obs_source_t *src = scenes.sources.array[i++];
 		OBSData data = obs_source_get_private_settings(src);
 		obs_data_release(data);