Memory access instructions which took the GPR_ZERO_DEREF_SAFE register
class (that was removed in #600) should check for the need of either an
offset (r13/rbp) or the SIB byte (r12/rsp). Some load/store instructions
would already take an index, thus already contain the SIB byte in this
case (see instructions which have a comment telling that the else branch
already contains an SIB byte). Non-indexed memory accesses lacked the
SIB byte check, which this patch adds.
b170b74b65