I am in Ragpicker's Square where I leapt through a portal which led me to a room without doors. A collector and 2 thugs extorted me for 100 gold and if I pick the option to fight them the collector will cast a spell called "Chromatic orb" which will make a black box appear and crash the game.

Should I reinstall or maybe download a patch?

It's actually worse, whenever a spell is cast the game will inevitably crash (though the time between crashes may differ from time to time).

GoG released a new version of the Planescape installer sometime in the last 24 hours.

What changes have been made, I do not know.

However, they do include http://bitpatch.com/ie_ddrawfix.html this (my) patch.
Which will help with crashing issues when casting spells. So re-download the GoG installer (~1 gb ) or grab my patch ( ~1.5 mb )