frontend/widgets: Fix integer overflow

If the crop values combined are larger than the width or height of the
source, an integer overflow will occur.

This fix converts the width/height values to int, and then clamps
any negative values to 0.

frontend/widgets/OBSBasicPreview.cpp

@@ -414,8 +414,9 @@ static vec2 GetItemSize(obs_sceneitem_t *item)
 
 		obs_sceneitem_get_scale(item, &scale);
 		obs_sceneitem_get_crop(item, &crop);
-		size.x = float(obs_source_get_width(source) - crop.left - crop.right) * scale.x;
-		size.y = float(obs_source_get_height(source) - crop.top - crop.bottom) * scale.y;
+		size.x = fmaxf(float((int)obs_source_get_width(source) - crop.left - crop.right), 0.0f);
+		size.y = fmaxf(float((int)obs_source_get_height(source) - crop.top - crop.bottom), 0.0f);
+		vec2_mul(&size, &size, &scale);
 	}
 
 	return size;