Follow-up CL to deflake RTCStatsIntegrationTest.GetStatsFromCallee

This is a follow-up to
https://webrtc-review.googlesource.com/c/src/+/295724.

Test is still failing sometimes. Add additional constraint.

Bug: webrtc:14952
Change-Id: Iddc2733459733c0f3e40aea303752f055cb865c5
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/295665
Reviewed-by: Henrik Boström <hbos@webrtc.org>
Commit-Queue: Henrik Boström <hbos@webrtc.org>
Auto-Submit: Johannes Kron <kron@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#39441}
diff --git a/pc/rtc_stats_integrationtest.cc b/pc/rtc_stats_integrationtest.cc
index 5cd3db9..f01d487 100644
--- a/pc/rtc_stats_integrationtest.cc
+++ b/pc/rtc_stats_integrationtest.cc
@@ -1173,6 +1173,7 @@
     auto inbound_stats =
         report->GetStatsOfType<RTCRemoteInboundRtpStreamStats>();
     return !inbound_stats.empty() &&
+           inbound_stats.front()->round_trip_time.is_defined() &&
            inbound_stats.front()->round_trip_time_measurements.is_defined();
   };
   EXPECT_TRUE_WAIT(GetStatsReportAndReturnTrueIfRttIsDefined(), kMaxWaitMs);