join: fix crash for '(' delimiter (#1057)

* As per commit b345448 for cut(1)
* The -t option expects a literal character to use as a delimiter for reading input files, but it was interpreted as a regex in split()
* Apply the same \Q & \E fix in the match as
* Small re-factor to avoid calling split() in both branches of ternary-operator

Author: mknos

bin/join

@@ -155,9 +155,10 @@ sub get_a_line {
   my $not_eof = defined(my $line = <$fh>);
   if ($not_eof) {
     chomp $line;
-    push (@$aref,
-	  defined $delimiter ?
-	  [split $delimiter, $line, -1] : [split ' ', $line, -1]);
+    my $d = $delimiter;
+    $d = ' ' unless defined $d;
+    my @parts = split /\Q$d\E/, $line, -1;
+    push @{ $aref }, [ @parts ];
   }
   else { push @$aref, undef }
   return $not_eof;