list_commands: only call git_exec_path if it is needed
list_commands: only call git_exec_path if it is needed

Even if it always needed

Signed-off-by: Alex Riesen <053ce55f4869b7f450d1d77b8f162c6f2bb9e137@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