No source event entry created for mousewheel in mouse.js

[tehbiga]

Was confused for some time why I could not process the mousewheel source event value when I realized that it's not being created even though a default of null is set earlier in the file.

https://github.com/liabru/matter-js/blob/014ef77d1e30b44cb65098c0efc9c9d623a40496/src/core/Mouse.js#L100-L103