Fix missing buffer size update.

src/pio_server.c

@@ -1156,6 +1156,7 @@ writeGribStream(size_t streamIdx, struct streamMapping *mapping, void **data_, s
             ;
           else
             rxWin[streamIdx].aggBuf = Malloc(aggBufSize);
+          rxWin[streamIdx].aggBufSize = aggBufSize;
         }
       namespaceSwitchSet(NSSWITCH_FILE_WRITE, NSSW_FUNC(aggBufAppend));
       /* write records to aggregation buffer */