added a try/finally block for added safety during rollback

Author: cbegin

src/main/java/org/apache/ibatis/executor/BaseExecutor.java

@@ -159,10 +159,13 @@ public void commit(boolean required) throws SQLException {
 
   public void rollback(boolean required) throws SQLException {
     if (!closed) {
-      clearLocalCache();
-      flushStatements();
-      if (required) {
-        transaction.rollback();
+      try {
+        clearLocalCache();
+        flushStatements();
+      } finally {
+        if (required) {
+          transaction.rollback();
+        }
       }
     }
   }