Don't print out a stacktrace when an error message is empty.
Don't print out a stacktrace when an error message is empty.

This was printing a lot of stacktraces for non-errors from GConf.

renatofilho/folks,GNOME/folks,renatofilho/folks,renatofilho/folks,pwithnall/folks,renatofilho/folks2,renatofilho/folks2,GNOME/folks,pwithnall/folks,pwithnall/folks,renatofilho/folks2,renatofilho/folks,renatofilho/folks2,GNOME/folks