Fix protocol error caused by redis-benchmark (#10236)

The protocol error was caused by the buggy `writeHandler` in `redis-benchmark.c`,
which didn't handle one of the cases, thereby repeating data, leading to protocol errors
when the values being sent are very long.

This PR fixes #10233, issue introduced by #7959

src/redis-benchmark.c

@@ -632,6 +632,9 @@ static void writeHandler(aeEventLoop *el, int fd, void *privdata, int mask) {
                         fprintf(stderr, "Error writing to the server: %s\n", strerror(errno));
                     freeClient(c);
                     return;
+                } else if (nwritten > 0) {
+                    c->written += nwritten;
+                    return;
                 }
             } else {
                 aeDeleteFileEvent(el,c->context->fd,AE_WRITABLE);