Common: Apply distinct to sql placeholders

GUIs.Common/frmSQLEditor.vb

@@ -209,6 +209,7 @@ Public Class frmSQLEditor
             ' noop
         Else
             Dim oPlaceholders = oPatterns.
+                Distinct().
                 Select(Function(pattern) New SQLEditor.Placeholder(pattern.Value, pattern.Value, pattern.Type, pattern.Value) With {.Pattern = pattern}).
                 ToList()
             GridPlaceholders.DataSource = oPlaceholders
@@ -232,7 +233,6 @@ Public Class frmSQLEditor
                         Throw New ApplicationException($"Der Platzhalter '{oWrapped}' wurde nicht ausgefüllt!")
                     End If
 
-
                     oSql = oSql.Replace(oWrapped, oPlaceholder.Value)
                 Next
             End If