forall: fix crash with no command

When callback= is used, optparse does not automatically initialize
The destination when a dest= is not specified.  Refine the test to
allow dest= options when callback= is used even when it seems like
it is otherwise redundant.

Bug: b/436611422
Change-Id: I5185f95cb857ca6d37357cac77fb117a83db9c0c
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/509861
Tested-by: Mike Frysinger <vapier@google.com>
Commit-Queue: Mike Frysinger <vapier@google.com>
Reviewed-by: Gavin Mak <gavinmak@google.com>

subcmds/forall.py

@@ -133,7 +133,7 @@ without iterating through the remaining projects.
 
     @staticmethod
     def _cmd_option(option, _opt_str, _value, parser):
-        setattr(parser.values, option.dest or "command", list(parser.rargs))
+        setattr(parser.values, option.dest, list(parser.rargs))
         while parser.rargs:
             del parser.rargs[0]
 
@@ -161,6 +161,7 @@ without iterating through the remaining projects.
         p.add_option(
             "-c",
             "--command",
+            dest="command",
             help="command (and arguments) to execute",
             action="callback",
             callback=self._cmd_option,