Clicking to ride a mob uses the item in your hand

Verification builds:
1.13.0.9 | Windows 10: Yes
1.13.0.9 | Android: Yes
1.12.0 | Windows 10: No

How to reproduce:

1. /summon boat

2. /give @p snowball

3. Hold the snowball and right-click to get in the boat

Expected results:
Snowball is not used

Actual results:
Snowball is used