gddo-server: enable log when running on GCE.

This fixes error when deploying to local machine.

Change-Id: I5d61c31f0c815ab3dfcaaaedf51903f7e1ec4954
Reviewed-on: https://go-review.googlesource.com/22804
Reviewed-by: Andrew Gerrand <adg@golang.org>
diff --git a/gddo-server/main.go b/gddo-server/main.go
index 5cb3ed5..f79bff3 100644
--- a/gddo-server/main.go
+++ b/gddo-server/main.go
@@ -302,7 +302,9 @@
 				log.Printf("ERROR db.IncrementPopularScore(%s): %v", pdoc.ImportPath, err)
 			}
 		}
-		gceLogger.LogEvent(resp, req, nil)
+		if gceLogger != nil {
+			gceLogger.LogEvent(resp, req, nil)
+		}
 
 		template := "dir"
 		switch {