Update location capabilites feature support checks

Author: nasc17

src/azure-cli/azure/cli/command_modules/rdbms/_flexible_server_location_capabilities_util.py

@@ -46,16 +46,20 @@ def _postgres_parse_list_capability(result):
     if not result:
         raise InvalidArgumentValueError("No available SKUs in this location")
 
-    offer_restricted = [feature for feature in result[0].supported_features if feature.name == "OfferRestricted"]
+    supported_features = result[0].supported_features if result[0].supported_features is not None else []
+    offer_restricted = [feature for feature in supported_features if feature.name == "OfferRestricted"]
+    restricted = offer_restricted[0].status if offer_restricted else None
+    zone_redundant = [feature for feature in supported_features if feature.name == "ZoneRedundantHa"]
+    geo_backup = [feature for feature in supported_features if feature.name == "GeoBackup"]
 
-    if offer_restricted[0].status == "Enabled":
+    if restricted == "Enabled":
         raise InvalidArgumentValueError("The location is restricted for provisioning of flexible servers. Please try using another region.")
 
-    if offer_restricted[0].status != "Disabled":
+    if restricted != "Disabled":
         raise InvalidArgumentValueError("No available SKUs in this location.")
 
-    single_az = result[0].zone_redundant_ha_supported != "Enabled"
-    geo_backup_supported = result[0].geo_backup_supported == "Enabled"
+    single_az = zone_redundant[0].status != "Enabled" if zone_redundant else True
+    geo_backup_supported = geo_backup[0].status == "Enabled" if geo_backup else False
 
     tiers = result[0].supported_server_editions
     tiers_dict = {}