JAVA-680: Fixing a regression introduced in the previous commit for this issue. In the case where the driver

is not connected to a replica set, like in mongos HA, still may need to ensure there is a master

Author: jyemin

src/main/com/mongodb/DBTCPConnector.java

@@ -269,7 +269,8 @@ private Response innerCall(final DB db, final DBCollection coll, final OutMessag
         boolean secondaryOk = !(readPref == ReadPreference.primary());
 
         _checkClosed();
-        if (!secondaryOk)
+        // Don't check master on secondary reads unless connected to a replica set
+        if (!secondaryOk || getReplicaSetStatus() == null)
             checkMaster( false, !secondaryOk );
 
         final MyPort mp = _myPort.get();