[Qemu-ppc] ppc vga output breakage since commit c3c1bb99

[BALATON Zoltan]

Hello,

Commit c3c1bb99d1c11978d9ce94d1bdcf0705378c1459 (exec: Respect 
as_tranlsate_internal length clamp) seems to break vga output with 
qemu-system-ppc on x86_64 host. Since this commit, the output window does 
not get to the OpenBIOS console but stays black. (Easy to reproduce by 
just starting qemu-system-ppc.)

The reason may be that this change has exposed another bug somewhere else 
but this is all quite obscure to me. Does anyone have any idea what could 
be wrong or where to look further. Any help is appreciated.

Thank you,
BALATON Zoltan