storage: Fix returning of locked objects from 'virStoragePoolObjListSearch'

storage: Fix returning of locked objects from 'virStoragePoolObjListSearch'

CVE-2023-3750

'virStoragePoolObjListSearch' explicitly documents that it's returning
a pointer to a locked and ref'd pool that maches the lookup function.

This was not the case as in commit 0c4b391e2a9 (released in
libvirt-8.3.0) the code was accidentally converted to use 'VIR_LOCK_GUARD'
which auto-unlocked it when leaving the scope, even when the code was
originally "leaking" the lock.

Revert the corresponding conversion and add a comment that this function
is intentionally leaking a locked object.

Fixes: 0c4b391e2a9
Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=2221851
Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>