ttffont-subset has some bug

[waldenlden]

I cut the font with ttffont.js ,but there are some problems with the subset I got. such as some glyphs not render. so i try to analyze the ttf file. And I found:

1. cmap
   if i cut 3 glyphs，its length should be 4； but i found it has full glyphs info

2. maxp
   we can see the length is wrong in maxp

And then i try to solve these problem,and i know the problem is that except for the glyph table, all other tables are directly obtained from the table contents of the full set. I don't know how to fix it，
I'd be very grateful if anyone could help me

[github-actions]

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