Don't desensitise quick filter widget while index is updating

[dccoder84]

I want to explain why I am annoyed by this commit. I just find it annoying to wait every time until indexing is finished. I understand of course why this commit was merged. The user shouldn't use the quick filter while the index is not complete. But see, I can use that time of waiting to already type a string. Also, even when the index isn't complete I still can get early results via quick filter. Additionally the user knows when the index is updating simply because the info is printed above the quick filter widget. Also keep in mind that synaptic is used by rather tech-savvy people because normal people are not interested in package details and simply use programs like Gnome Software to install programs.

[Lanchon]

i second this.

instead of desensitizing during update, just update quick search results when the index finishes updating (as if the query string had just been changed).