Fix dyld opcode *_ADD_ADDR_IMM_SCALED error detection.

Summary:
Move the check for malformed REBASE_OPCODE_ADD_ADDR_IMM_SCALED and
BIND_OPCODE_DO_BIND_ADD_ADDR_IMM_SCALED opcodes after the immediate
has been applied to the SegmentOffset. This fixes specious errors
where SegmentOffset is pointing between two sections when trying to
correct the SegmentOffset value.

Update the regression tests to verify the proper error message.

Reviewers: pete, ab, lhames, steven_wu, jhenderson

Reviewed By: pete

Subscribers: hiraditya, dexonsmith, rupprecht, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D75629