custom commands broken in Ubuntu 18.04

Repeatable using Ubunut 18.04 standard repositories, and also guake_3.0.5-1_all.deb from [launchpad](https://launchpad.net/ubuntu/bionic/+package/guake)

**Building from the 3.0.4.1 source code is the current fix.**
This was done building with the files from: `git clone https://github.com/gsemet/guake.git`

_Issues_
1. Crashes when custom commands file is entered. The fix from [Fix crash when changing command file](https://github.com/gsemet/guake/commit/74fa3c2ce13cadf0c90203faffcc69a2c3963b49) works only in preventing a crash. This issue was originally posted [here](https://github.com/Guake/guake/issues/1229).
2. The above fix only stops guake from crashing, while it does not 'remember' or 'cache' the file. *It does show up in dconf editor in apps.guake.general.cusotom-command-file. Once the file is entered in Preferences, guake does not make a menu entry or show the file when preferences is opened again; and this is the same whether or not the program and/or Ubuntu has been restarted.