[PATCH pve-manager] ui: sdn: dns selector: keep an untouched edit dialog clean

[Hannes Laimer <h.laimer@proxmox.com>]

The selector starts out on the empty string, and once its store has
loaded an empty selection reads back as null. Both mean that no server
is picked, but the dirty tracking told them apart, so just opening a
zone edit dialog enabled its reset button and let an unchanged form be
submitted.

Signed-off-by: Hannes Laimer <h.laimer@proxmox.com>
---
just noticed here because zone edit kept being marked as dirty, this
could also make sense in ComboGrid directly (don't think we ever
actually differentiate between `null` and `''`?)

 www/manager6/form/SDNDnsSelector.js | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/www/manager6/form/SDNDnsSelector.js b/www/manager6/form/SDNDnsSelector.js
index 7a134541..9d36e8d7 100644
--- a/www/manager6/form/SDNDnsSelector.js
+++ b/www/manager6/form/SDNDnsSelector.js
@@ -8,6 +8,10 @@ Ext.define(
         valueField: 'dns',
         displayField: 'dns',
 
+        isEqual: function (value1, value2) {
+            return String(value1 ?? '') === String(value2 ?? '');
+        },
+
         initComponent: function () {
             var me = this;
 
-- 
2.47.3