autotest: add missing `next` in cmptrash()

this doesn't really matter, as the branches are mutually exclusive
anyway, but still.

amends 01329bdf.

src/run-tests.pl

@@ -631,6 +631,7 @@ sub cmptrash($$$)
 		if (!defined($ph)) {
 			print STDERR "Missing message $bn:".mn($num)."\n";
 			$ret = 1;
+			next;
 		}
 		if ($ph) {
 			print STDERR "Message $bn:".mn($num)." is placeholder\n";