fix pan/zoom bug

was missing an rts on update_palette

this happened to fall through to keycheck
which if timing was wrong would dutifully process the viewport
change and return to update_palette's caller

which in turn was -not- expecting to reset the outer loop

fixed

mandel.s

@@ -1094,6 +1094,8 @@ done:
     and #$f0
     adc palette + 3
     sta COLOR2
+
+    rts
 .endproc
 
 .proc update_speed

todo.md

@@ -1,7 +1,5 @@
 things to try:
 
-* fix the pan/zoom bug where it doesn't reset loop right :(
-
 * add some preset viewports that can be switched via number keys (1, 2, 3 etc)
 
 * patch the entire expanded-ram imul8xe on top of imul8 to avoid the 3-cycle thunk penalty :D