JSON: fix JsonReadOnlyProxyArray not iterating on a null or missing field

- should return immediately if the backing field is null or missing

Author: KrzysFR

SnowBank.Core/Data/JSON/Proxies/JsonReadOnlyProxyArray.cs

@@ -156,7 +156,7 @@ public IEnumerator<TProxy> GetEnumerator()
 // the result would change if there are additional items in the array
 if (!m_value.TryGetCount(out var count))
 {
-if (m_value.GetJsonUnsafe())
+if (m_value.GetJsonUnsafe().IsNullOrMissing())
 {
 yield break;
 }