Bugfix: the check to see if a node was already shared into a namespace

was incorrect.

Author: cure

Diff for: sharing.go

@@ -21,12 +21,15 @@ func (h *Headscale) AddSharedMachineToNamespace(m *Machine, ns *Namespace) error
 		return errorSameNamespace
 	}
 
-	sharedMachine := SharedMachine{}
-	if err := h.db.Where("machine_id = ? AND namespace_id", m.ID, ns.ID).First(&sharedMachine).Error; err == nil {
+	sharedMachines := []SharedMachine{}
+	if err := h.db.Where("machine_id = ? AND namespace_id = ?", m.ID, ns.ID).Find(&sharedMachines).Error; err != nil {
+		return err
+	}
+	if len(sharedMachines) > 0 {
 		return errorMachineAlreadyShared
 	}
 
-	sharedMachine = SharedMachine{
+	sharedMachine := SharedMachine{
 		MachineID:   m.ID,
 		Machine:     *m,
 		NamespaceID: ns.ID,