Replaces a fatal log message with an early return in CallbackVisitor.

This should allow the fuzz test to make further progress.

PiperOrigin-RevId: 540652890

quiche/http2/adapter/callback_visitor.cc

diff --git a/quiche/http2/adapter/callback_visitor.cc b/quiche/http2/adapter/callback_visitor.cc
index 64f0ed6..81e57db 100644
--- a/quiche/http2/adapter/callback_visitor.cc
+++ b/quiche/http2/adapter/callback_visitor.cc
@@ -471,7 +471,11 @@
 }
 
 bool CallbackVisitor::OnMetadataEndForStream(Http2StreamId stream_id) {
-  QUICHE_LOG_IF(DFATAL, current_frame_.hd.flags != kMetadataEndFlag);
+  if (current_frame_.hd.flags != kMetadataEndFlag) {
+    QUICHE_VLOG(1) << "Expected kMetadataEndFlag during call to "
+                   << "OnMetadataEndForStream!";
+    return true;
+  }
   QUICHE_VLOG(1) << "OnMetadataEndForStream(stream_id=" << stream_id << ")";
   if (callbacks_->unpack_extension_callback) {
     void* payload;