If table tag is not 0x3f, we expect a value between 0 and 62. If this is
not the case, exit with errors.
* src/sfnt/sfwoff2/c: Check whether table tag makes sense.
* src/sfnt/woff2tags.c: Return 0 if tag is out of bounds.
Change `KnownTags' to a function (`woff2_known_tags'). This avoids
introducing a global constant array. This function returns the specified
index without *any* checks. The caller must ensure that `index' is
within array limits.
* src/sfnt/sfwoff2.c (woff2_open_font): Change `KnownTags[...]' notation
to `woff2_known_tags( ... )'.
* src/sfnt/woff2tags.c: Perform changes.
* src/sfnt/woff2tags.h: Update definitions.
Add constants required for WOFF2, and known table tags as defined in the
specification. See
https://www.w3.org/TR/WOFF2/#table_dir_format
for details.
* src/sfnt/woff2tags.c, src/sfnt/woff2tags.h: New files.
Nikhil Ramakrishnan