If get_maintainer is not given any filename arguments on the command line,
the standard input is read for a patch.
But checking if a VCS has a file named &STDIN is not a good idea and fails.
Verify the nominal input file is not &STDIN before checking the VCS.
Fixes: 4cad35a7ca ("get_maintainer.pl: reduce need for command-line option -f")
Reported-by: Christopher Covington <[email protected]>
Signed-off-by: Joe Perches <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>