Metal: Don't render into an empty view.

Change-Id: I4f407ab77854fa50d3b30e0bf54c365aee51923d
Bug: webrtc:10040
Reviewed-on: https://webrtc-review.googlesource.com/c/111782
Reviewed-by: Anders Carlsson <andersc@webrtc.org>
Commit-Queue: Peter Hanspers <peterhanspers@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#25759}

sdk/objc/components/renderer/metal/RTCMTLVideoView.m

@@ -141,6 +141,10 @@
     return;
   }
 
+  if (CGRectIsEmpty(view.bounds)) {
+    return;
+  }
+
   RTCMTLRenderer *renderer;
   if ([videoFrame.buffer isKindOfClass:[RTCCVPixelBuffer class]]) {
     RTCCVPixelBuffer *buffer = (RTCCVPixelBuffer*)videoFrame.buffer;