skip set languageDictionary for canvas on reload

Earlier versions of macOS didn't reset some graphics context settings on reload. Doesn't seem to be an issue anymore, but just in case it changes again, keep the language defaults as they were when canvas module *first* loaded, even after reloads.

extensions/canvas/libcanvas.m

@@ -4025,7 +4025,7 @@ int luaopen_hs_libcanvas(lua_State* L) {
                                  metaFunctions:nil    // or module_metaLib
                                objectFunctions:userdata_metaLib];
 
-    languageDictionary = defineLanguageDictionary() ;
+    if (!languageDictionary) languageDictionary = defineLanguageDictionary() ;
 
     [skin registerPushNSHelper:pushHSCanvasView         forClass:"HSCanvasView"];
     [skin registerLuaObjectHelper:toHSCanvasViewFromLua forClass:"HSCanvasView"