am: format is in $patch_format, not parse_patch
am: format is in $patch_format, not parse_patch

The error message given when the patch format was not recognized was
wrong, since the variable checked was $parse_patch rather than
$patch_format. Fix by checking the non-emptyness of the correct
variable.

Signed-off-by: Giuseppe Bilotta <6010d7f2c049984f25cd19568d4ace2cc46b0817@gmail.com>
Signed-off-by: Junio C Hamano <a6723cc3f76163bf7adb636a73ac3b0ceb3e6b9b@pobox.com>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git