[woff2] Copy un-transformed tables to sfnt stream. Copy un-transformed tables to the sfnt stream. * src/sfnt/sfwoff2.c: (WRITE_SFNT_BUF): New macro. (write_buf): New function. Extend memory of `dst' buffer and copy bytes from `src'. (compute_ULong_sum): New function. Calculate checksum of table. (reconstruct_font): Change `FT_Byte* sfnt' to `FT_Byte** sfnt_bytes'. This has been done because we reallocate memory to `sfnt' multiple times, which may change the pointer value of `sfnt'. This new pointer must be propogated back to the caller. Same reason for using a double pointer in `write_buf'. * src/sfnt/woff2tags.h (WOFF2_DEFAULT_MAX_SIZE): New macro used for overflow checking.