[psaux, cff] Protect against nested `seac' calls. * include/freetype/internal/psaux.h (T1_Decoder), src/cff/cffgload.h (CFF_Decoder): Add `seac' boolean variable. * src/cff/cffgload.c (cff_operator_seac, cff_decoder_parse_charstrings), src/psaux/t1decode.c (t1operator_seac, t1_decoder_parse_charstrings): Use it.