fix: update grpc upload error diagnostics to be tolerant of receiving…

… an error if no request has been sent (#2732)

google-cloud-storage/src/main/java/com/google/cloud/storage/GapicBidiUnbufferedWritableByteChannel.java

@@ -367,7 +367,9 @@ public void onError(Throwable t) {
                 tmp.getCode(),
                 tmp.getMessage(),
                 tmp.getReason(),
-                ImmutableList.of(lastWrittenRequest),
+                lastWrittenRequest != null
+                    ? ImmutableList.of(lastWrittenRequest)
+                    : ImmutableList.of(),
                 null,
                 context,
                 t);