Use minimal timer access and diagnose failed video image transforms

tools/chatgui/src/call_video_decoder.cpp

@@ -188,7 +188,10 @@ int CallVideoDecoder::receive(call_video_frame& f, QImage& image) {
             uint8_t* planes[4] = {output.bits(), nullptr, nullptr, nullptr}; int strides[4] = {(int)output.bytesPerLine(), 0, 0, 0};
             if (sws_scale(m->scale, pixels->data, pixels->linesize, 0, pixels->height, planes, strides) != pixels->height)
                 result = AVERROR_INVALIDDATA;
-            else image = f.format.rotation ? output.transformed(QTransform().rotate(f.format.rotation)) : output;
+            else {
+                image = f.format.rotation ? output.transformed(QTransform().rotate(f.format.rotation)) : output;
+                if (image.isNull()) result = AVERROR(ENOMEM);
+            }
         }
     }
     av_frame_free(&copied); av_frame_free(&decoded);