Revert "server: Make the indexingStatuses argument required"

This reverts commit 7740c0a.

Author: dimitrovmaksim

server/index-node/src/resolver.rs

@@ -139,7 +139,7 @@ impl<S: Store> IndexNodeResolver<S> {
                     .collect(),
                 _ => unreachable!(),
             })
-            .unwrap();
+            .unwrap_or_else(Vec::new);
 
         let infos = self
             .store

server/index-node/src/schema.graphql

@@ -21,7 +21,7 @@ type Query {
   indexingStatusesForSubgraphName(
     subgraphName: String!
   ): [SubgraphIndexingStatus!]!
-  indexingStatuses(subgraphs: [String!]!): [SubgraphIndexingStatus!]!
+  indexingStatuses(subgraphs: [String!]): [SubgraphIndexingStatus!]!
   proofOfIndexing(
     subgraph: String!
     blockNumber: Int!