Fix optimize_textures.sh

[EGYT5453]

I don't know when it stopped working, but now it gives the following error:

find: warning: ‘-name’ matches against basenames only, but the given pattern contains a directory separator (‘/’), thus the expression will evaluate to false all the time. Did you mean ‘-wholename’?

Changing it from find -name '../*.png' to find .. -name '*.png' fixed it for me.

[SmallJoker]

I suppose this script was intended to be run from the git root like so:

bash util/optimize_textures.sh

A proper solution would be to use

SCRIPT_DIR=`realpath "$(dirname "$0")"`
find "$SCRIPT_DIR/.." -name '*.png' -print0 | xargs -0 optipng -o7 -zm1-9 -nc -strip all -clobber

EDIT2: I think this issue was caused by an untested change resulting from the following comment: #2808 (comment)