AbstractSubscription#onError must call the onError method of the observer

JAVARS-216

Author: jstewart148

driver-async/src/main/com/mongodb/async/client/MongoIterableSubscription.java

@@ -65,8 +65,12 @@ boolean checkCompleted() {
 
     @Override
     void postTerminate() {
-        if (batchCursor != null) {
-            batchCursor.close();
+        try {
+            if (batchCursor != null) {
+                batchCursor.close();
+            }
+        } catch (Exception e) {
+            // do nothing
         }
     }