setup.c: stop prefix_pathspec() from looping past the end of string
setup.c: stop prefix_pathspec() from looping past the end of string

The code assumes that the string ends at either `)` or `,`, and does
not handle the case where strcspn() returns length due to end of
string.  So specifying ":(top" as pathspec will cause the loop to go
past the end of string.

Signed-off-by: Andrew Wong <284ec9141727d0bb92378cf0a865336c51a1e413@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