Enable LAYER_MOD_TEXT_FR layer in fp editor as it should.

It also fixes a crash when changing visibility of other fp texts..

pcbnew/widgets/appearance_controls.cpp

@@ -371,6 +371,7 @@ static std::set<int> s_allowedInFpEditor =
             LAYER_PADS_TH,
             LAYER_MOD_VALUES,
             LAYER_MOD_REFERENCES,
+            LAYER_MOD_TEXT_FR,
             LAYER_MOD_TEXT_INVISIBLE,
             LAYER_GRID
         };