Fix a typo that causes struct->fields corruption
Fix a typo that causes struct->fields corruption

BLK_SKIP skips by the size of REBVAL, while "fields" has a width of
Struct_Field.

This fixes:
>> a: make struct! [ rebval [2] v struct! [rebval [3] nv int32 i] sv]
>> recycle
>> mold a
Program received signal SIGSEGV, Segmentation fault.

draegtun/ren-c,giuliolunati/ren-c,hostilefork/rebol,codebybrett/ren-c,hostilefork/rebol,hostilefork/rebol,draegtun/ren-c,rgchris/ren-c,hostilefork/rebol,rgchris/ren-c,giuliolunati/ren-c,rgchris/ren-c,rgchris/ren-c,codebybrett/ren-c,kealist/ren-c,draegtun/ren-c,hostilefork/rebol,mbk/ren-c,mbk/ren-c,kealist/ren-c,giuliolunati/ren-c,kealist/ren-c,codebybrett/ren-c,codebybrett/ren-c,draegtun/ren-c,giuliolunati/ren-c,giuliolunati/ren-c,mbk/ren-c,rgchris/ren-c,hostilefork/rebol,kealist/ren-c,mbk/ren-c,draegtun/ren-c,draegtun/ren-c,codebybrett/ren-c,kealist/ren-c,codebybrett/ren-c,kealist/ren-c