handle_revision_arg: reset "dotdot" consistently

When we are parsing a range like "a..b", we write a temporary NUL over the first ".", so that we can access the names "a" and "b" as C strings. But our restoration of the original "." is done at inconsistent times, which can lead to confusing results. For most calls, we restore the "." after we resolve the names, but before we call verify_non_filename(). This means that when we later call add_pending_object(), the name for the left-hand "a" has been re-expanded to "a..b". You can see this with: git log --source a...b where "b" will be correctly marked with "b", but "a" will be marked with "a...b". Likewise with "a..b" (though you need to use --boundary to even see "a" at all in that case). To top off the confusion, when the REVARG_CANNOT_BE_FILENAME flag is set, we skip the non-filename check, and leave the NUL in place. That means we do report the correct name for "a" in the pending array. But some code paths try to show the whole "a...b" name in error messages, and these erroneously show only "a" instead of "a...b". E.g.: $ git cherry-pick HEAD:foo...HEAD:foo error: object d95f3ad14dee633a758d2e331151e950dd13e4ed is a blob, not a commit error: object d95f3ad14dee633a758d2e331151e950dd13e4ed is a blob, not a commit fatal: Invalid symmetric difference expression HEAD:foo (That last message should be "HEAD:foo...HEAD:foo"; I used cherry-pick because it passes the CANNOT_BE_FILENAME flag). As an interesting side note, cherry-pick actually looks at and re-resolves the arguments from the pending->name fields. So it would have been visibly broken by the first bug, but the effect was canceled out by the second one. This patch makes the whole function consistent by re-writing the NUL immediately after calling verify_non_filename(), and then restoring the "." as appropriate in some error-printing and early-return code paths. Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>