log-filestore: fix file descriptor leak

In the case we exceed the number of simultaneously open
file we can reach a state were we will not close the file
after writing.

Thanks to Steve Grubb <sgrubb@redhat.com> for the analysis.

src/log-filestore.c

@@ -461,6 +461,7 @@ static int LogFilestoreLogger(ThreadVars *tv, void *thread_data, const Packet *p
             if (FileGetMaxOpenFiles() > 0) {
                 StatsIncr(tv, aft->counter_max_hits);
             }
+            ff->fd = -1;
         }
     /* we can get called with a NULL ffd when we need to close */
     } else if (data != NULL) {