We've been open-coding virStringListFreeCount for cleaning up
the completion list we're building. This had the advantage of
zeoring the pointer afterwards, which is no longer needed
now that we compile the list in 'tmp' instead of 'ret'.
Since all our lists are NULL-terminated anyway, switch to using
virStringListFree via the VIR_AUTOSTRINGLIST macro.
Fixes nearly impossible NULL dereferences in
virshNWFilterBindingNameCompleter
virshNWFilterNameCompleter
virshNodeDeviceNameCompleter
virshNetworkNameCompleter
virshInterfaceNameCompleter
virshStoragePoolNameCompleter
virshDomainNameCompleter
which jumped on the error label after a failed allocation
and a possible one in
virshStorageVolNameCompleter
which jumped there when we fail to fetch the list of volumes.
Signed-off-by: Ján Tomko <jtomko@redhat.com>