* Fix crash trying to enter particle mode when the particle modifier
is disabled in the stack.
* Fix redraw being very slow due to the draw function causing the
object to be recalculated on each redraw (through PE_draw_object).
* Removed the system where PE_get_current would automatically create
the particle edit, this would run from poll() functions, which gave
all kinds of issues, now it only creates the data on enter/exit
and switching active particle system.
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