glib/gpoll: Remove if conditional

The original ready < nhandles - 1 can be re-written as ready + 1 < nhandles
which is the same confition that we are checking on the first
itteration of the for loop. This means we can remove the if statement
and let the for loop check the code.

This also has the side effect of removing an invalid check as
WAIT_OBJECT_0 was not subtracted from ready in the if statement.

Signed-off-by: Alistair Francis <alistair.francis@xilinx.com>