use computed values in src/gtx/curseswindows.c

use computed values in src/gtx/curseswindows.c

compiling failed, because of -Wunused-value.
Use the return code of wstandout and wstandend and pass
it upwards.

Reviewed-on: http://gerrit.openafs.org/3344
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
(cherry picked from commit 03ab065e0ccf291d45a93b7d63c022bcad3aac34)

Change-Id: I4623ba9c00ea19b33d73831f6f11ba2d2e32b1a0
Reviewed-on: http://gerrit.openafs.org/3511
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>