vos: don't free stack garbage on error

vos: don't free stack garbage on error

If wantExtendedInfo is true, then pntr is used uninitialized.
In the other case, UV_ListVolumes will have set it to NULL
before doing anything (even if it returns an error), so this
free() is dead anyway.

Found-by: clang static analyzer
Reviewed-on: http://gerrit.openafs.org/5164
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Simon Wilkinson <sxw@inf.ed.ac.uk>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
(cherry picked from commit 619b420903c99e48618db0d2f12085111573f279)

Change-Id: Icd76d3ac160ccb04b05445552a9e6d04f053efbb
Reviewed-on: http://gerrit.openafs.org/5227
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>