[KPhotoAlbum] Annotation performance improvments

[Johannes Zarl-Zierl]

Hi,

Am Dienstag, 14. Jänner 2020, 01:02:10 CET schrieb Robert Krawitz:
> I've created a new 'annotation-performance' branch with these
> improvements.  If everyone agrees that they're safe, I think it would
> be good to get this into 5.6; it will greatly improve performance of
> annotation for people with a lot of images and groups.

So far, there's three commits:
252bc62b Improve calculation of max text height
49a8a47e Improve performance of annotation dialog
b7f378e6 Speed up computing new selection

The two last ones seem safe on first sight.
The first one (252bc62b) computes consistently too low numbers, leading to 
clipped text. Returning grps.length() - 1 instead leads to occasional wasted 
space, but seems otherwise lead to correct results.

  Johannes