#289 fix the error handling when xa transaction error in prepare

src/main/java/com/actiontech/dble/backend/mysql/nio/handler/NewConnectionRespHandler.java

@@ -22,21 +22,21 @@ public class NewConnectionRespHandler implements ResponseHandler {
     private ReentrantLock lock = new ReentrantLock();
     private Condition initiated = lock.newCondition();
 
-    public BackendConnection getBackConn() throws IOException{
+    public BackendConnection getBackConn() throws IOException {
         lock.lock();
         try {
             if (backConn == null) {
                 initiated.await();
             }
-            if(backConn == null){
+            if (backConn == null) {
                 throw new IOException("get backend connection error ");
             }
             return backConn;
         } catch (InterruptedException e) {
             LOGGER.warn("getBackConn " + e);
             return null;
-        } catch(IOException e){
-            throw  e;
+        } catch (IOException e) {
+            throw e;
         } finally {
             lock.unlock();
         }