fix: update gRPC Bidi resumable upload to have more robust error message generation

[BenWhitehead]

onError can be called before a message is written to the stream, make sure we are accounting for the possibility that lastWrittenRequest can be null.

The fix prevents the following type of NPE from happening

Feb 18, 2025 10:39:15 PM io.grpc.internal.SerializingExecutor run SEVERE: Exception while executing runnable io.grpc.internal.ClientCallImpl$ClientStreamListenerImpl$1StreamClosed@5b549e5c java.lang.NullPointerException	at com.google.common.base.Preconditions.checkNotNull(Preconditions.java:904)	at com.google.common.collect.SingletonImmutableList.<init>(SingletonImmutableList.java:42)	at com.google.common.collect.ImmutableList.of(ImmutableList.java:101)	at com.google.cloud.storage.GapicBidiUnbufferedWritableByteChannel$BidiObserver.onError(GapicBidiUnbufferedWritableByteChannel.java:355)	at com.google.api.gax.rpc.ApiStreamObserverAdapter.onErrorImpl(ApiStreamObserverAdapter.java:61)	at com.google.api.gax.rpc.StateCheckingResponseObserver.onError(StateCheckingResponseObserver.java:84)	at com.google.api.gax.tracing.TracedResponseObserver.onError(TracedResponseObserver.java:104)	at com.google.api.gax.grpc.ExceptionResponseObserver.onErrorImpl(ExceptionResponseObserver.java:84)	at com.google.api.gax.rpc.StateCheckingResponseObserver.onError(StateCheckingResponseObserver.java:84)	at com.google.api.gax.grpc.GrpcDirectStreamController$ResponseObserverAdapter.onClose(GrpcDirectStreamController.java:148)	at io.grpc.PartialForwardingClientCallListener.onClose(PartialForwardingClientCallListener.java:39)	at io.grpc.ForwardingClientCallListener.onClose(ForwardingClientCallListener.java:23)	at io.grpc.ForwardingClientCallListener$SimpleForwardingClientCallListener.onClose(ForwardingClientCallListener.java:40)	at com.google.api.gax.grpc.ChannelPool$ReleasingClientCall$1.onClose(ChannelPool.java:569)	at io.grpc.PartialForwardingClientCallListener.onClose(PartialForwardingClientCallListener.java:39)	at io.grpc.ForwardingClientCallListener.onClose(ForwardingClientCallListener.java:23)	at io.grpc.ForwardingClientCallListener$SimpleForwardingClientCallListener.onClose(ForwardingClientCallListener.java:40)	at com.google.cloud.storage.it.GrpcPlainRequestLoggingInterceptor$1$1.onClose(GrpcPlainRequestLoggingInterceptor.java:92)	at io.grpc.internal.ClientCallImpl.closeObserver(ClientCallImpl.java:564)	at io.grpc.internal.ClientCallImpl.access$100(ClientCallImpl.java:72)	at io.grpc.internal.ClientCallImpl$ClientStreamListenerImpl$1StreamClosed.runInternal(ClientCallImpl.java:729)	at io.grpc.internal.ClientCallImpl$ClientStreamListenerImpl$1StreamClosed.runInContext(ClientCallImpl.java:710)	at io.grpc.internal.ContextRunnable.run(ContextRunnable.java:37)	at io.grpc.internal.SerializingExecutor.run(SerializingExecutor.java:133)	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)	at java.lang.Thread.run(Thread.java:750)