Avoid Empty Conditions list due to removed recipients - filter cannot be edited about quickfilters

[RealRaven2000]

I will log this as enhancement. Hopefully I will be able to address it once we have quickFilters compatible with Thunderbird 78.

[RealRaven2000]

As a quick workaround: should we return to the assistant where the filter template is selected if the conditions list will be empty? One could show a message: with the current filter template "by recipients", no meaningful filter conditions can be created, please select a different template.

[RealRaven2000]

Here is my solution. Instead of creating a nonsensical filter that cannot be edited and wasting the users time, I display this message:

Trial version (Tb78):
quickFilters-wx-4.5pre7.zip

Trial version (Tb68):
quickFilters-wx-5.2pre30.zip

[RealRaven2000]

Implemented in releases 4.5 + 5.2