[geany/geany] 6cee28: Get rid of warning in on_file_notify()

[Matthew Brush]

  Branch: refs/heads/master
  Home:   https://github.com/geany/geany

  Commit: 6cee28d677d7fd11058de7f4da5562475bd14d1a
      https://github.com/geany/geany/commit/6cee28d677d7fd11058de7f4da5562475bd14d1a
  Author: Matthew Brush <matt at geany.org>
  Date:   2011-11-13 (Sun, 13 Nov 2011)

  Changed paths:
    M src/dialogs.c

  Log Message:
  -----------
  Get rid of warning in on_file_notify()

Works around the issue discussed in commit 1e54fb6 by using the file
chooser's property accessor function.
Rename on_file_notify() to better explain its purpose.