Fix random segfaulting related to TTF lookup tables, especially on shift+R.

The segfaulting occured when a TTF Font contains a GSUB table with a
Lookup type other than one. This caused us to initialize a data
structure that represents the lookup table, but never fill it in.

Rarely, one of these tables would hava field initalized to 1 or 2. In
that case, we'd try to free associated data that was never properly
initialized, and we'd crash.

The fix was to intialize the data structures before use.