sftp_init_reply_ok: fix small memory leak (libfuse#198)

The leak was identified with ASAN: configure the project with
meson -Db_sanitize=address to reproduce.

sshfs.c

@@ -1596,12 +1596,14 @@ static int sftp_init_reply_ok(struct conn *conn, struct buffer *buf,
  }
 
  do {
- char *ext;
- char *extdata;
+ char *ext = NULL;
+ char *extdata = NULL;
 
  if (buf_get_string(&buf2, &ext) == -1 ||
  buf_get_string(&buf2, &extdata) == -1) {
  buf_free(&buf2);
+ free(ext);
+ free(extdata);
  return -1;
  }
 
@@ -1621,6 +1623,9 @@ static int sftp_init_reply_ok(struct conn *conn, struct buffer *buf,
  if (strcmp(ext, SFTP_EXT_FSYNC) == 0 &&
  strcmp(extdata, "1") == 0)
  sshfs.ext_fsync = 1;
+
+ free(ext);
+ free(extdata);
  } while (buf2.len < buf2.size);
  buf_free(&buf2);
  }