[Ohrrpgce] SVN: teeemcee/10493 Split out SpriteSliceUpdate from sliceedit: crazy-bad encapsulation viol

[subversion at HamsterRepublic.com]

teeemcee
2018-07-28 09:55:06 -0700 (Sat, 28 Jul 2018)
295
Split out SpriteSliceUpdate from sliceedit: crazy-bad encapsulation violation

This also fixes clamping of frame number.

Also be much more careful about handling NULL TextSliceData.assetfile pointers
without crashing.
(NULL string ptrs are OK for some FB string functions but will crash others)
---
U   wip/sliceedit.bas
U   wip/slices.bas
U   wip/slices.bi