pcapng: free up the section table when closing the file.

Change-Id: Iad70785b2baf178c16d1d333479590d3909150e5
Reviewed-on: https://code.wireshark.org/review/36983
Reviewed-by: Guy Harris <gharris@sonic.net>

wiretap/pcapng.c

@@ -3088,6 +3088,7 @@ pcapng_close(wtap *wth)
     pcapng_t *pcapng = (pcapng_t *)wth->priv;
 
     pcapng_debug("pcapng_close: closing file");
+    g_array_free(pcapng->sections, TRUE);
     g_array_free(pcapng->interfaces, TRUE);
 }