Add LookupType method to fix custom roles upgrade bug

If upgrading from 4.4.1 or previous and database has a custom role the
4.4.2 upgrade step fails as the 5.0.4 code expects the LookupType column
to exist in the database.

Add a LookupType method that attempts to call LookupType on its parent
class and if there is no result default to the only possible value for
older databases.

lib/RT/CustomRole.pm

@@ -74,6 +74,27 @@ Returns table name for records of this class
 
 sub Table {'CustomRoles'}
 
+=head2 LookupType
+
+Returns the lookup type for records of this class
+
+=cut
+
+sub LookupType {
+    my $self = shift;
+
+    # LookupType column might not exist in older databases
+    my $type = '';
+    eval {
+        $type = $self->SUPER::LookupType(@_);
+    };
+    # if no type found default to the only possibility for older databases
+    $type = 'RT::Queue-RT::Ticket'
+        unless $type;
+
+    return $type;
+}
+
 =head2 Create PARAMHASH
 
 Create takes a hash of values and creates a row in the database: