Plug file descriptor leak.

Change-Id: I882cc5c264fdf97452c84bd5cea0e5d56bd6eb45
Reviewed-on: https://code.wireshark.org/review/11753
Reviewed-by: Guy Harris <guy@alum.mit.edu>

wiretap/file_access.c

@@ -2280,6 +2280,7 @@ wtap_dump_open_tempfile_ng(char **filenamep, const char *pfx,
 	fh = wtap_dump_file_fdopen(wdh, fd);
 	if (fh == NULL) {
 		*err = errno;
+		close(fd);
 		g_free(wdh);
 		return NULL;	/* can't create file */
 	}