qemu: snapshot: go through cleanup on error

A recent commit added an error check for too-nested backing chains
followed by a return, even though errors above jump to cleanup.
Signed-off-by: NJán Tomko <jtomko@redhat.com>
Fixes: b168fa88Reviewed-by: NDaniel P. Berrangé <berrange@redhat.com>
Reviewed-by: NAndrea Bolognani <abologna@redhat.com>

src/qemu/qemu_driver.c

@@ -14654,7 +14654,7 @@ qemuDomainSnapshotCreateInactiveExternal(virQEMUDriverPtr driver,
             snapdisk->src->format = VIR_STORAGE_FILE_QCOW2;
 
         if (qemuDomainStorageSourceValidateDepth(defdisk->src, 1, defdisk->dst) < 0)
-            return -1;
+            goto cleanup;
 
         /* creates cmd line args: qemu-img create -f qcow2 -o */
         if (!(cmd = virCommandNewArgList(qemuImgPath,