The penultimate element of `ranges_x86` array has an incorrect value: it
should be *at least* 0x2f0, which is the minimum size of an extended
context.

Fix this by setting it to 0x440, which is the minimum size of an
extended context *with* CONTEXT_I386_XSTATE.  This is consistent with
`ranges_amd64`, the penultimate element of which has the minimum size of
an extended context *with* CONTEXT_AMD64_XSTATE.

Note that the incorrect value does not always lead to a test failure,
since check_changes_in_range_() effectively ignores range `start`s that
are not in order.  Reproducing the failure requires a system with a
sufficiently large XSAVE area; specifically, the following condition is
necessary for check_changes_in_range_() to pick up the wrong value:

    0x2cc < 0x294 + src_ex->XState.Length - sizeof(XSTATE).