[Ohrrpgce] SVN: teeemcee/10968 Fix not being able to import or edit whole spriteset for hero spritset 0

[subversion at HamsterRepublic.com]

teeemcee
2019-02-12 22:01:22 -0800 (Tue, 12 Feb 2019)
292
Fix not being able to import or edit whole spriteset for hero spritset 0

Caused by the hidden spriteset template slice in the slice collection which
had a copy of that sprite set. I've replaced it with an asset sprite slice
with blank filename, which is now allowed and won't throw an error.
---
U   wip/common.rbas
U   wip/data/spriteset_browser.slice
U   wip/slices.bas