[MCPE-12564] When swapping world from creative to survival, it completly clears my inventory.

What I expected to happen was...:
When I switch world type from creative to survival I expected my survival inventory NOT to change.

What actually happened was...:
Instead, it completly cleared my inventory.

Steps to Reproduce:
1. Start a creative world.
2. Get some items in your survival inventory
3. Switch gamemode to survival
4. Survival inventory is empty!