[KYUUBI #1056] [BUG] Log error if no current spark sql engine is created.

Issue:  https://github.com/apache/incubator-kyuubi/issues/1056

### _Why are the changes needed?_
Log an error message if no current spark sql engine is created.

### _How was this patch tested?_
- [ ] Add some test cases that check the changes thoroughly including negative and positive cases if possible

- [ ] Add screenshots for manual tests if appropriate

- [x] [Run test](https://kyuubi.readthedocs.io/en/latest/develop_tools/testing.html#running-tests) locally before make a pull request

Closes #1423 from jadireddi/1056-no-currEng.

Closes #1056

a8d0443d [Jagadesh Adireddi] refactor
565d41a4 [Jagadesh Adireddi] [KYUUBI #1056] [BUG] Log error if no current spark sql engine is created.

Authored-by: Jagadesh Adireddi <jadiredd@conviva.com>
Signed-off-by: fwang12 <fwang12@ebay.com>

externals/kyuubi-spark-sql-engine/src/main/scala/org/apache/kyuubi/engine/spark/SparkSQLEngine.scala

@@ -158,12 +158,15 @@ object SparkSQLEngine extends Logging {
         // blocking main thread
         countDownLatch.await()
       } catch {
-        case e: KyuubiException if currentEngine.isDefined =>
-          val engine = currentEngine.get
-          engine.stop()
-          val event = EngineEvent(engine).copy(diagnostic = e.getMessage)
-          EventLoggingService.onEvent(event)
-          error(event, e)
+        case e: KyuubiException => currentEngine match {
+          case Some(engine) =>
+            engine.stop()
+            val event = EngineEvent(engine).copy(diagnostic = e.getMessage)
+            EventLoggingService.onEvent(event)
+            error(event, e)
+          case _ => error("Current SparkSQLEngine is not created.")
+        }
+
       }
     } catch {
       case t: Throwable => error(s"Failed to instantiate SparkSession: ${t.getMessage}", t)