When opening some file format (let's say *.tif) and then trying to save as *.kra file (or any other format different from the original one in fact), when I choose the desired target format from the list, the extension of the actual file doesn't get changed (see attachment "not_changed_extension.png"). It's quite inconvenient and annoying, since when I hit OK, the file is not even saved as *.tif.kra, but it remains simple *.tif (see attachment "not_changed_extension2.png"). [sorry for the PL texts in screens, but the popup windows look the same in any language, so I hope u get what's going on]

The "fun" doesn't end here though, since even when I manually delete the wrong extension (with dot) in the "Save as..." window, leaving only file name and hit OK on saving, the file is saved as *.kra... but with double dot (see attachment "double_dot.png").

This must be some kind of regression in saving mechanism, since it never happened to me in previous versions of Krita.

Reproducible: Always

Steps to Reproduce:
a)
1. Open some file.
2. Try to save it with different extension.
b)
1. Open some file.
2. Try to save it with different extension, removing the original extension and the dot manually in the "Save as..." window.

Actual Results:  
The extension remains the same/saves with double dot.

Expected Results:  
Extension should follow the options chosen in "Save as..." window and be saved with single dot (unless ofc. there was a dot in the file name, but u get the point).