"call already closed" exceptions in fnapi

These are logged several times when running Python wordcount on the Flink runner. They don't seem to affect pipeline execution, but they are annoying.

 
python -m apache_beam.examples.wordcount \--input /path/to/inputfile \
\--output /path/to/write/counts \
\--runner FlinkRunner

java.lang.IllegalStateException: call already closed
at org.apache.beam.vendor.grpc.v1p43p2.com.google.common.base.Preconditions.checkState(Preconditions.java:510)
at org.apache.beam.vendor.grpc.v1p43p2.io.grpc.internal.ServerCallImpl.closeInternal(ServerCallImpl.java:214)
at org.apache.beam.vendor.grpc.v1p43p2.io.grpc.internal.ServerCallImpl.close(ServerCallImpl.java:207)
at org.apache.beam.vendor.grpc.v1p43p2.io.grpc.stub.ServerCalls$ServerCallStreamObserverImpl.onCompleted(ServerCalls.java:395)
at org.apache.beam.runners.fnexecution.state.GrpcStateService.close(GrpcStateService.java:63)
at org.apache.beam.sdk.fn.server.GrpcFnServer.close(GrpcFnServer.java:156)
at org.apache.beam.runners.fnexecution.control.DefaultJobBundleFactory$WrappedSdkHarnessClient.$closeResource(DefaultJobBundleFactory.java:642)
at org.apache.beam.runners.fnexecution.control.DefaultJobBundleFactory$WrappedSdkHarnessClient.close(DefaultJobBundleFactory.java:642)
at org.apache.beam.runners.fnexecution.control.DefaultJobBundleFactory$WrappedSdkHarnessClient.unref(DefaultJobBundleFactory.java:658)
at org.apache.beam.runners.fnexecution.control.DefaultJobBundleFactory$WrappedSdkHarnessClient.access$400(DefaultJobBundleFactory.java:589)
at org.apache.beam.runners.fnexecution.control.DefaultJobBundleFactory.lambda$createEnvironmentCaches$3(DefaultJobBundleFactory.java:212)
at org.apache.beam.vendor.guava.v26_0_jre.com.google.common.cache.LocalCache.processPendingNotifications(LocalCache.java:1809)
at org.apache.beam.vendor.guava.v26_0_jre.com.google.common.cache.LocalCache$Segment.runUnlockedCleanup(LocalCache.java:3462)
at org.apache.beam.vendor.guava.v26_0_jre.com.google.common.cache.LocalCache$Segment.postWriteCleanup(LocalCache.java:3438)
at org.apache.beam.vendor.guava.v26_0_jre.com.google.common.cache.LocalCache$Segment.clear(LocalCache.java:3215)
at org.apache.beam.vendor.guava.v26_0_jre.com.google.common.cache.LocalCache.clear(LocalCache.java:4270)
at org.apache.beam.vendor.guava.v26_0_jre.com.google.common.cache.LocalCache$LocalManualCache.invalidateAll(LocalCache.java:4909)
at org.apache.beam.runners.fnexecution.control.DefaultJobBundleFactory.close(DefaultJobBundleFactory.java:319)
at org.apache.beam.runners.fnexecution.control.DefaultExecutableStageContext.close(DefaultExecutableStageContext.java:43)
at org.apache.beam.runners.fnexecution.control.ReferenceCountingExecutableStageContextFactory$WrappedContext.closeActual(ReferenceCountingExecutableStageContextFactory.java:212)
at org.apache.beam.runners.fnexecution.control.ReferenceCountingExecutableStageContextFactory$WrappedContext.access$200(ReferenceCountingExecutableStageContextFactory.java:188)
at org.apache.beam.runners.fnexecution.control.ReferenceCountingExecutableStageContextFactory.release(ReferenceCountingExecutableStageContextFactory.java:177)
at org.apache.beam.runners.fnexecution.control.ReferenceCountingExecutableStageContextFactory.scheduleRelease(ReferenceCountingExecutableStageContextFactory.java:136)
at org.apache.beam.runners.fnexecution.control.ReferenceCountingExecutableStageContextFactory.access$300(ReferenceCountingExecutableStageContextFactory.java:48)
at org.apache.beam.runners.fnexecution.control.ReferenceCountingExecutableStageContextFactory$WrappedContext.close(ReferenceCountingExecutableStageContextFactory.java:208)
at org.apache.beam.runners.flink.translation.functions.FlinkExecutableStageFunction.$closeResource(FlinkExecutableStageFunction.java:268)
at org.apache.beam.runners.flink.translation.functions.FlinkExecutableStageFunction.close(FlinkExecutableStageFunction.java:373)
at org.apache.flink.api.common.functions.util.FunctionUtils.closeFunction(FunctionUtils.java:41)
at org.apache.flink.runtime.operators.BatchTask.run(BatchTask.java:524)
at org.apache.flink.runtime.operators.BatchTask.invoke(BatchTask.java:360)
at org.apache.flink.runtime.taskmanager.Task.runWithSystemExitMonitoring(Task.java:958)
at org.apache.flink.runtime.taskmanager.Task.restoreAndInvoke(Task.java:937)
at org.apache.flink.runtime.taskmanager.Task.doRun(Task.java:766)
at org.apache.flink.runtime.taskmanager.Task.run(Task.java:575)

Imported from Jira [BEAM-14354](https://issues.apache.org/jira/browse/BEAM-14354). Original Jira may contain additional context.
Reported by: ibzib.