Ensure icon is always set for recent files actions

Previously the icon was only set in one code path. As a result the icons were not set when the whole recent files list was loaded. This commit fixes that.

This also fixes folders having the generic application/octet icon set by not simply matching on the file ending. Remote files are handled explicitly by always setting a specific icon. This is to be consistent with the icon handling in the recent items list of Kate's and Okular's welcome view.