PS: maybe universal-ctags's `matlab.c` was removed for historical reasons and the devs forgot about it, and it should just be added back replacing Geany's own modified version? I can test if the upstream version works too.
I just had a look at that file and it seems to be more complete (it seems to do the right thing, plus it also parses classes and variables), so maybe it's a better idea to just pull that file instead, and ignore this PR (unless there's a reason to use geany_matlab.c instead of the one universal-ctags provides).
I naïvely tried to integrate that file into Geany myself and failed miserably, so maybe I'll leave this parked until someone with more experience has time to have a look at this. (There's no rush at the moment; it's not like having poor tag detection in Matlab is such a big deal; it's just that I thought this was going to be a quick fix that wouldn't be bothering any dev until after the holidays.)