return 0 when field is zero (#8955)

ydb/core/viewer/protos/viewer.proto

@@ -441,19 +441,19 @@ message TStorageGroupInfo {
     string Kind = 7;
     string MediaType = 8;
     string ErasureSpecies = 9;
-    uint64 AllocationUnits = 10;
+    optional uint64 AllocationUnits = 10;
     string State = 11;
-    uint64 MissingDisks = 12; // Degraded
-    uint64 Used = 13;
-    uint64 Limit = 14;
-    uint64 Available = 15;
-    float Usage = 16;
-    uint64 Read = 17;
-    uint64 Write = 18;
-    float DiskSpaceUsage = 19;
-    uint64 LatencyPutTabletLog = 20;
-    uint64 LatencyPutUserData = 21;
-    uint64 LatencyGetFast = 22;
+    optional uint64 MissingDisks = 12; // Degraded
+    optional uint64 Used = 13;
+    optional uint64 Limit = 14;
+    optional uint64 Available = 15;
+    optional float Usage = 16;
+    optional uint64 Read = 17;
+    optional uint64 Write = 18;
+    optional float DiskSpaceUsage = 19;
+    optional uint64 LatencyPutTabletLog = 20;
+    optional uint64 LatencyPutUserData = 21;
+    optional uint64 LatencyGetFast = 22;
     repeated TStorageVDisk VDisks = 30;
 }