Throw error when can not terminate che task

Signed-off-by: Roman Nikitenko <rnikiten@redhat.com>

extensions/eclipse-che-theia-plugin-ext/src/plugin/che-task-impl.ts

@@ -41,6 +41,7 @@ export class CheTaskImpl implements CheTask {
         if (runner) {
             return await runner.kill(taskInfo);
         }
+        throw new Error(`Failed to terminate Che command: ${taskInfo.config.label}: the corresponging executor is not found`);
     }
 
     async fireTaskExited(event: TaskExitedEvent): Promise<void> {