make maxval work better near p8 precision limits

vacuum_gambit.p8

@@ -423,9 +423,13 @@ end
 
 function vertmeter(x0,y0,x1,y1,val,maxval,cols)
  if ((val <= 0) or (maxval <= 0)) return
+ if val < 0x0.001 or maxval < 0x0.001 then
+  val *= 16
+  maxval *= 16
+ end
  val=min(val, maxval)
  local h = y1-y0
- local px = val/maxval * h \ 1
+ local px = val*h/maxval \ 1
  local ncols = #cols
  local firstcol = ((h-px)*ncols\h)+1
  local lastbottom = y0+(h*firstcol\ncols)