#325 window-icon: avod unwanted access to an extraneous file.

[Dmitry Butskoy]

Currently window-icon option has the default value of "yad".
It causes yad to always check at startup time for a file named "yad" in the current directiry.

It is possible that a file with such a name exists in the homedir , but is not an icon at all. (Fe. some another yad binary, copied here for tests, or anything else occasionally match the same name). In this case, a warning appears on stderr:

(yad:10199): Gtk-WARNING **: 20:24:12.408: Error loading icon from file 'yad':
    Couldn’t recognize the image file format for file “yad”

The proposed patch changes default value to NULL, with the proper fixes for main.c and html.c .