Blender Git Loki

Fix T49461: Dynamic paint wetmap flickers.

Regression from rBa4a968f, we would adjust current point's wetness without actually protecting it
in new multi-threaded context, leading to concurrent access mess.

Now delay applying wetness reduction to current point to end of function, allows us to avoid having
to lock current point twice together with neighbor one (and reducing spinlock awainting too).

To be backported to 2.78a.