Segfault when low memory event fires

To reproduce (On Nexus 7 (2012) at least, not sure how to trigger a low memory event on other devices)

• Open Minecraft PE

• Go to Settings

• Skins

• Custom

• When the browser for skins shows up, hit the back button

• Once back in MCPE, hit the Multitask button

Expected:

• MCPE gets placed in background

Actual:

• MCPE force-closes with this stack trace: https://gist.github.com/zhuowei/e9a43e30ba268dfdf192

It looks like the low memory handler tried to destroy the LevelRenderer, but since no world has been loaded, the LevelRenderer was null and the destructor segfaulted.