Make scanline spacing symmetric

(8,20) skip set left gaps of 4,8,4,8,4,4 -- uneven, since the trailing
two gaps were both 4 instead of alternating. Removing two slots exactly
opposite each other in the 8-slot cycle (0 and 16) is the most even
spacing achievable while keeping every line on a multiple of
SCANLINE_PERIOD: gaps come out 4,4,8,4,4,8, symmetric.

subwave_nowplaying.star

@@ -558,7 +558,12 @@ def _glitch_scanlines():
     # positions instead of the last two in the run -- which left an 8px
     # gap with nothing in it at the bottom of every cycle -- spreads the
     # resulting two, slightly-larger gaps across the full height instead.
-    SCANLINE_SKIP = (8, 20)  # keeps a line at y=28, near the bottom edge
+    # Removing two slots exactly opposite each other (half the 8-slot
+    # cycle apart) is the most even spacing achievable while keeping every
+    # line on a multiple of SCANLINE_PERIOD: gaps come out 4,4,8,4,4,8 --
+    # symmetric, vs. e.g. removing two adjacent-ish slots which leaves an
+    # uneven 4,8,4,8,4,4 pattern.
+    SCANLINE_SKIP = (0, 16)
     tall = ART_SLOT + SCANLINE_PERIOD
     lines = []
     for y in range(tall):