Fix missing return value in rtc_event_field_parser

Bug: webrtc:11933
Change-Id: Ia9c10293f61cb30c4d2ec29edf53f0ed53a4e8ef
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/234740
Reviewed-by: Artem Titov <titovartem@webrtc.org>
Commit-Queue: Björn Terelius <terelius@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#35172}

logging/rtc_event_log/events/rtc_event_field_encoding_parser.cc

@@ -113,6 +113,9 @@ uint64_t EventParser::ReadSingleValue(FieldType field_type) {
       SetError();
       return 0;
   }
+  RTC_NOTREACHED();
+  SetError();
+  return 0;
 }
 
 void EventParser::ReadDeltasAndPopulateValues(