python - fe: Only attempt to extract tuple counts when rmsg is not None.

Log Message:
-----------
Only attempt to extract tuple counts when rmsg is not None.
(Test NULL message producing queries per pq fix.)

Modified Files:
--------------
fe/src:
tracenull.py (r1.24 -> r1.25)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/python/fe/src/tracenull.py.diff?r1=1.24&r2=1.25)
fe/test:
tracenull.py (r1.12 -> r1.13)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/python/fe/test/tracenull.py.diff?r1=1.12&r2=1.13)