Relax checks on link targets in create templates

Prior to this change it wasn't possible to copy or add links to anything
other than tickets in a CreateTicket template.

This change removes a template-specific check on what might be a valid
link and trusts that the AddLink method knows how to validate what was
passed to it.

lib/RT/Action/CreateTickets.pm

@@ -1213,14 +1213,15 @@ sub PostProcess {
 
                 } elsif ( $link !~ m/^\d+$/ ) {
                     my $key = "create-$link";
-                    if ( !exists $T::Tickets{$key} ) {
+                    if ( exists $T::Tickets{$key} ) {
+                        $RT::Logger->debug( "Building $type link for $link: "
+                                . $T::Tickets{$key}->Id );
+                        $link = $T::Tickets{$key}->Id;
+                    }
+                    else {
                         $RT::Logger->debug(
-                            "Skipping $type link for $key (non-existent)");
-                        next;
+                            "Building $type link for $link");
                     }
-                    $RT::Logger->debug( "Building $type link for $link: "
-                            . $T::Tickets{$key}->Id );
-                    $link = $T::Tickets{$key}->Id;
                 } else {
                     $RT::Logger->debug("Building $type link for $link");
                 }