Seems to be introduced by 99e5024e97.
The crash is caused by the difference in the expected alignment
of the `uiPopupMenu` which is 16 bytes and the actual alignment
returned by the `MEM_mallocN()` which is 8 bytes due to the memory
head.
Now made it so that `MEM_new()` can be used for types with any
alignment.
Differential Revision: https://developer.blender.org/D16375