Fix NPE in UIMA AS aggregate which occurs while recovering from Cas Multiplier failure

The following exception happens when UIMA AS aggregate tries to recover from a colocated CM failure:

java.lang.NullPointerException
at org.apache.uima.aae.controller.AggregateAnalysisEngineController_impl.finalStep(AggregateAnalysisEngineController_impl.java:1819)
at org.apache.uima.aae.controller.AggregateAnalysisEngineController_impl.abortProcessingCas(AggregateAnalysisEngineController_impl.java:1041)
at org.apache.uima.aae.controller.AggregateAnalysisEngineController_impl.process(AggregateAnalysisEngineController_impl.java:1099)
at org.apache.uima.aae.handler.HandlerBase.invokeProcess(HandlerBase.java:118)
at org.apache.uima.aae.handler.input.ProcessResponseHandler.cancelTimerAndProcess(ProcessResponseHandler.java:108)
at org.apache.uima.aae.handler.input.ProcessResponseHandler.handleProcessResponseWithCASReference(ProcessResponseHandler.java:387)
at org.apache.uima.aae.handler.input.ProcessResponseHandler.handle(ProcessResponseHandler.java:666)
at org.apache.uima.aae.handler.HandlerBase.delegate(HandlerBase.java:149)
at org.apache.uima.aae.handler.input.ProcessRequestHandler_impl.handle(ProcessRequestHandler_impl.java:982)
at org.apache.uima.aae.spi.transport.vm.UimaVmMessageListener.onMessage(UimaVmMessageListener.java:107)
at org.apache.uima.aae.spi.transport.vm.UimaVmMessageDispatcher$1.run(UimaVmMessageDispatcher.java:70)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
at org.apache.uima.aae.UimaAsThreadFactory$1.run(UimaAsThreadFactory.java:110)
at java.lang.Thread.run(Thread.java:619)