LoggingAnnotator: don't output to trace file if there is no platform

This is a revert of a small chunk of
https://chromium-review.googlesource.com/c/angle/angle/+/1761163 that is
suspect to cause weird failures on the GPU FYI waterfall in Debug on
Windows, maybe because the many disk writes are too slow.

BUG=chromium:997667
TBR=jmadill@chromium.org

Change-Id: Ifb799d2ed90682e55e5cc7c0ce21d2598bf30c9e
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1768371
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>

src/libANGLE/LoggingAnnotator.cpp

@@ -54,7 +54,10 @@ void LoggingAnnotator::logMessage(const gl::LogMessage &msg) const
                 UNREACHABLE();
         }
     }
-    gl::Trace(msg.getSeverity(), msg.getMessage().c_str());
+    else
+    {
+        gl::Trace(msg.getSeverity(), msg.getMessage().c_str());
+    }
 }
 
 }  // namespace angle