fix(sharded): fix count in fetchSockets() method (#523)

If `fetchSockets()` is called shortly after the adapter was
initialized, the server count may still return 0, causing this to fail
with "timeout reached: only 0 responses received out of -1".

lib/cluster-adapter.ts

@@ -436,7 +436,7 @@ export abstract class ClusterAdapter extends Adapter {
     ]);
     const expectedResponseCount = serverCount - 1;
 
-    if (opts.flags?.local || expectedResponseCount === 0) {
+    if (opts.flags?.local || expectedResponseCount <= 0) {
       return localSockets;
     }