Fix user query filter display

[Alkarex]

fix #6360

[math-GH]

Quite better as before PR.

What I think is not good working right now:
"Empty filter" text, if there is no expression and the main stream chosen.

If you select this query f.e. in the view of favorites, than it would jump to the main stream.
If you would select this query in the main stream, but you have the "show only unread articles, then it would show unread and read articles after reloading.

One more thought: Does it make sense to keep the "no filter" text? I would say that every query is a valid filter.

If the expression is mandatory then we should mark it as mandatory (via require attribute)

[Alkarex]

The search expression is not mandatory. We could indeed remove the no filter. Let's keep that for another PR, as it is less urgent for 1.24.0.