Fix slight inaccuracy in test 3_F7_05_2

[OFFTKP]

Needs cwd/cdq/cqo to sign extend into RDX/EAX/AX for imul to do what is described, for example in

; Negative * Negative
mov ax, -128
imul word [r8 + 8 * 0 + 0]
ofcfmerge

dx:ax is not negative, unless if we do cwd

[Sonicadvance1]

Nice catch! Thanks for the improvement!