MT#57070 ignore undef enum.default_val

while provisioning.voip_preference_enums.default_val
is supposed to be a flag variable, it is NULL for
some prefs.

we prevent a 500 error when editing such value in this
case now.

Change-Id: Idc5e0f1f0de93f9d0b6645982025c8b45bae1ec4
(cherry picked from commit dd9d57c33b)

lib/NGCP/Panel/Utils/Preferences.pm

@@ -1486,7 +1486,7 @@ sub create_preference_form {
         if ($c->stash->{preference}->first) {
             $preselected_value = $c->stash->{preference}->first->value unless ($c->stash->{preference_meta}->data_type eq 'blob');
         } else {
-            my $default_val = first { $_->default_val == 1 } @{ $enums };
+            my $default_val = first { $_->default_val; } @{ $enums };
             $preselected_value = $default_val ? $default_val->value : undef;
         }
     } elsif ($c->stash->{preference_meta}->max_occur == 1) {