The problem was not happening with the master code of
gimpdisplayshell-tool-events.c, but I encountered it in gimp-2-10 with
the layer picking code.
Even then, it still works, but I need to protect calls to
gdk_event_get_axis() to avoid CRITICALs.

(cherry picked from commit b1fe1675)

Note: this was not absolutely necessary on master (no CRITICALs), but I
can see that the same piece of code applies, so I may as well sync.