git-p4: narrow the scope of exceptions caught when parsing an int

The current code traps all exceptions around some code which parses an
integer, and then talks to Perforce.

That can result in errors from Perforce being ignored. Change the code
to only catch the integer conversion exceptions.

Signed-off-by: Luke Diamand <luke@diamand.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-p4.py

@@ -948,7 +948,7 @@ def p4ChangesForPaths(depotPaths, changeRange, requestedBlockSize):
         try:
             (changeStart, changeEnd) = p4ParseNumericChangeRange(parts)
             block_size = chooseBlockSize(requestedBlockSize)
-        except:
+        except ValueError:
             changeStart = parts[0][1:]
             changeEnd = parts[1]
             if requestedBlockSize: