#103 Create default mld (main.mld) file if file in OpenLastFileUsed does not exist.

[madproton]

If option "Open last file used" is selected(default) and the file does not exist, an error is shown and the window will not show a tab control. This may be confusing to first time users.

Solution: Create the default main.mld file if "Open last file used" is selected and the last opened file no longer exist.