ListBox: refuse to give values before we are loaded

If we are not loaded,
we don't know our field type,
so cannot give values with the right type

Change-Id: I372b77647ec8ff7428b67cca72fdd89e5e147a32

forms/source/component/ListBox.cxx

@@ -1058,6 +1058,9 @@ namespace frm
 
     ValueList OListBoxModel::impl_getValues() const
     {
+        if (!isLoaded())
+            return ValueList();
+
         const sal_Int32 nFieldType = getValueType();
 
         if ( !m_aConvertedBoundValues.empty() && m_nConvertedBoundValuesType == nFieldType )