checkpatch: improve parse_email signature checking

Bare email addresses with non alphanumeric characters require escape
quoting before being substituted in the parse_email routine.

e.g. Reported-by: syzbot+bbd8e9a06452cc48059b@syzkaller.appspotmail.com

Do so.

Link: http://lkml.kernel.org/r/1518631805.3678.12.camel@perches.com
Signed-off-by: Joe Perches <joe@perches.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

scripts/checkpatch.pl

@@ -1075,7 +1075,7 @@ sub parse_email {
 	} elsif ($formatted_email =~ /(\S+\@\S+)(.*)$/) {
 		$address = $1;
 		$comment = $2 if defined $2;
-		$formatted_email =~ s/$address.*$//;
+		$formatted_email =~ s/\Q$address\E.*$//;
 		$name = $formatted_email;
 		$name = trim($name);
 		$name =~ s/^\"|\"$//g;