Without this patch, the following exception is thrown when the touch
screen is used: TypeError: e.getBoundingClientRect is not a function.
No touch events arrive in the engine.
From my testing, this PR fixes the issue and behaves as expected.
Tested with godot-demo-projects/misc/multitouch_view/, emscripten 1.39.8
and Firefox mobile emulator as well as FF on Android
(cherry picked from commit 5134317afc)