Enable btnLink only when valid selections are made

Added EnableBtnLink method to control btnLink's enabled state based on lbxWMIndex and lbxQuelle1 selections or txtManIndexwert input. btnLink is now disabled by default and updated dynamically via selection change handlers.

ToolCollection/frmNIVerknuepfungen.Designer.vb

@@ -1763,6 +1763,7 @@ Partial Class frmNIVerknuepfungen
         '
         'btnLink
         '
+        Me.btnLink.Enabled = False
         Me.btnLink.Image = Global.ToolCollection.My.Resources.Resources.link
         Me.btnLink.ImeMode = System.Windows.Forms.ImeMode.NoControl
         Me.btnLink.Location = New System.Drawing.Point(409, 167)

ToolCollection/frmNIVerknuepfungen.vb

@@ -560,6 +560,7 @@ Public Class frmNIVerknuepfungen
                     Next
                 End If
 
+                EnableBtnLink()
 
             End If
 
@@ -1393,6 +1394,13 @@ Public Class frmNIVerknuepfungen
         End Try
 
     End Function
+
+    Private Sub EnableBtnLink()
+        btnLink.Enabled =
+            lbxWMIndex.SelectedItems.Count > 0 And
+            (lbxQuelle1.SelectedItems.Count > 0 OrElse txtManIndexwert.Text <> "")
+    End Sub
+
     Private Sub btnLink_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnLink.Click
         ' wenn im ListView ein Element selektiert wurde
         If Me.lvwVerknuepfungen.SelectedItems.Count > 0 Then
@@ -2829,6 +2837,8 @@ Public Class frmNIVerknuepfungen
         Else
             grbFilterDB.Enabled = True
         End If
+
+        EnableBtnLink()
     End Sub
     Private Sub txtGrundgeruest_check_Click(sender As System.Object, e As System.EventArgs) Handles txtGrundgeruest_check.Click
         Me.txtCheckIndexSQL.Text = "SELECT COUNT(*) FROM [%view] WHERE "
@@ -3522,7 +3532,14 @@ Public Class frmNIVerknuepfungen
         If _selectedIndex_Type Is Nothing = False Then
             visinvisible_Vektor_ins_State()
         End If
+
+        EnableBtnLink()
     End Sub
+
+    Private Sub lbxQuelle1_SelectedIndexChanged(sender As Object, e As EventArgs) Handles lbxQuelle1.SelectedIndexChanged
+        EnableBtnLink()
+    End Sub
+
     Sub visinvisible_Vektor_ins_State()
         If _selectedIndex_Type.StartsWith("Vektor") Then
             Me.rbvkt_add.Visible = True