Help Fluid oddities at <= 4 particles

[slimedev]

although each particle still jitters a bit and meanders.

Apologies not to follow up for so long. This erratic movement was my fault because I was applying random forces to particles as an anti-stick and anti-pancaking measure. (especially pancakey after splatting on the ground after falling from high height)
Could probably be improved by locking the "fake brownian motion" to normal/ anti-normal, since I don't want to bother with precise math of "detect any flattened particles". Although maybe that would be easier by measuring their density and not some wonky planar math.

Oh well. No Bug, My Bad.