Fix incorrect mapping in cmap during ttf parse with format=6

[aidos]

A bug with the ttf parser was erroneously creating a bad cmap when format=6.

To be 100% honest, all this font stuff is a little outside my sphere of knowledge but I ran into this issue while extracting fonts from a PDF.

In my case I was seeing a final font with B->B, C->F, F->F (the pattern was the same across a number of fonts). After the fix I correctly get B->B, F->F.

The bug itself is a simple iteration typo.

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[frank-trampe]

It looks good to me.