wish: remove the pre-loading of the mru file and don't pre-fill the 'Source image' field

Why:
The app now first tries to pre-load the last used sprite sheet. Which is saved/logged in the ini logfile within the [mru] section. But in the case this file is missing, a warning message correctly pops up.
I'm not sure why it even tries to load a previous loaded sprite sheet, but maybe I'm overlooking something.
So maybe this pre-load previous sprite sheet function plus the pre-filling of the ' Source image' field can be removed?

Repro:
Given I have loaded a sprite sheet
When I close the app
And remove/relocate the sprite sheet
And reopen app
Then it first shows the error popup message: "Could not find file, '<path+filename>'.
When I click the popup OK button
Then the slicer app start correctly
But the mentioned path and file are loaded and shown in 'Source image' 

Expected behavior:
When I restart the app, it does not try to pre-load the last loaded sprite sheet (logged as mru), as the intention of restarting the app is to load and slice a new sprite sheet.

Misc:
Ini Logfile section app tries to load:

[mru]
filename=<path>\<filename.ext