Replace CHECK(x && y) with two separate CHECK() calls

That way, the debug printout will tell us which of x and y that was false.

BUG=none

Review-Url: https://codereview.webrtc.org/2988153003
Cr-Commit-Position: refs/heads/master@{#19297}
diff --git a/webrtc/modules/video_coding/frame_object.cc b/webrtc/modules/video_coding/frame_object.cc
index 25d0e29..1d858fc 100644
--- a/webrtc/modules/video_coding/frame_object.cc
+++ b/webrtc/modules/video_coding/frame_object.cc
@@ -102,7 +102,8 @@
   timestamp = first_packet->timestamp;
 
   VCMPacket* last_packet = packet_buffer_->GetPacket(last_seq_num);
-  RTC_CHECK(last_packet && last_packet->markerBit);
+  RTC_CHECK(last_packet);
+  RTC_CHECK(last_packet->markerBit);
   // http://www.etsi.org/deliver/etsi_ts/126100_126199/126114/12.07.00_60/
   // ts_126114v120700p.pdf Section 7.4.5.
   // The MTSI client shall add the payload bytes as defined in this clause