[BUG][PLAYER] Outline on skill panel buttons is "sticky" if skillset empty.

[namida]

If a level has no skills in the skillset, then if Pause, Fast Forward, Nuke, Clear Physics Mode or Directional Select is activated, the outline around the respective button will remain present even when the relevant mode is deactivated again.

For this to trigger, the level must outright have no skills in the panel full stop - it isn't enough to just have no skills remaining. Examples of such levels would be Mild 1 "Just Walk" or Wimpy 22 "Fast Enough?" from Lemmings Plus I, or Coarse 5 "Tactical Drops" from Lemmings Plus Omega II.

Not tested:
- Does this affect the compact panel too? I have only confirmed this bug on the full-width panel.
- Is the bug present in the Shimmier experimental version? I have only tested on the stable version.

[namida]

Have pushed a commit 786f4ef which fixes this bug.