0.91 - beta2: impossible to delete companion-file master-extensions in options

[osenboz]

Hey there,
i just started trying xnview, and it seems to be just what i'm searching for...
(so thanks for the great software!)

however, while testing some of it's features within the new beta-release,
i noticed that in the "file-list" > "companion-files" option it is impossible to
delete or edit any of the master-extensions! this also applies to newly
added master-extensions... once they are there you can only delete them
by explicitly removing them from the .ini file, but not within xnview itself
(companion-extensions can be edited as expected...)

[osenboz]

Hey,
i just found that the master-extensions actually go away if you
delete all companion-file extensions and then close and re-open the 'settings' !

[xnview]

i'll add a context menu to delete entries