Fix #35082: Blender Freeze when change smoke domain setting

Issue was introduced by svn rev56273 and was caused by
both smokeModifier_do and smokeModifier_reset (which is
called from smokeModifier_do) do mutex lock/unlock.
This lead to quite undefined behavior caused by the same
thread released mutex twice.

Solved by not locking mutex from inside routines calling
from smokeModifier_process -- mutex is locked in parent
function anyway.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@56306 954f8c5b-7b00-dc11-b283-0030488c597c