When deleting a window make sure to update the progress bar code.

[David Hampton]

Log Message:
-----------
When deleting a window make sure to update the progress bar code.
Fixes a crash when you delete the last window and then try to save.
>From Phil Longstaff <plongstaff at newearth.org>.

Tags:
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gnucash-gnome2-dev

Modified Files:
--------------
    gnucash/src/gnome-utils:
        gnc-main-window.c
        gnc-window.c
        gnc-window.h