PANEL_FP_EDITOR_FIELD_DEFAULTS: fix incorrect behavior.

One could not change the default layers for new fp texts

Fixes https://gitlab.com/kicad/code/kicad/-/issues/20505

pcbnew/dialogs/panel_fp_editor_field_defaults.cpp

@@ -127,7 +127,8 @@ public:
     long GetValueAsLong( int row, int col ) override { return m_items[row].m_Layer; }
     void SetValueAsLong( int row, int col, long value ) override
     {
-        if( col == 2 )
+        if( col == GetNumberCols() - 1 )    // only last column uses a long value
+                                            // (probably useless test)
             m_items[row].m_Layer = static_cast<PCB_LAYER_ID>( value );
     }