Update BackendEntryIterator.java

Fix bug: gremlin语句执行超时 将导致内存泄漏statement未释放

fix apache#1639

hugegraph-core/src/main/java/com/baidu/hugegraph/backend/store/BackendEntryIterator.java

@@ -123,7 +123,7 @@ protected final boolean reachLimit(long count) {
         } catch (Throwable e) {
             try {
                 this.close();
-            } catch (Exception ex) {
+            } catch (Throwable ex) {
                 LOG.warn("Failed to close backend entry iterator for interrupted query", ex);
             }
             throw e;