crouching while using jettpack with empty fuel crashes the server

[TheUtopianPlayz]

Please make sure your issue complies with these guidelines:

• • [x] Server Software must be the official PMMP w/o vanilla patching plugins (i.e. TeaSpoon)
• • [x] Issue must have not been reported previously
• • [x] Make sure you are on the latest version of PMMP & PiggyCustomEnchants
• • [x] Have a detailed title.

Link to crashdump: https://crash.pmmp.io/view/4705781

Extra Information

pretty much as the title says, when ever u try to use jetpack while ur fuel is empty it causes the server to crash, im on the latest stable version of pmmp

[Aericio]

I also added a cooldown to prevent an issue where spamming shift key would allow you to infinitely fly.

If you feel that the cooldown is too long (default is 25), go to extra_data.json and modify jetpack.enableAmount.