main cycle only if the len passed is equal to 0. If end address
overflows use last possible address as the end address.
Based on: discussion on arm@
MFC after: 1 month
to if (len == 0).
The length is supposed to be unsigned, so len - 1 < 0 won't happen except
if len == 0 anyway, and it would return 0 when it shouldn't, if len was
> INT_MAX.
Spotted out by: Channa <channa kad gmail com>
