Fix - shiny color swap (#1183)

* return a list of errors if something is wrong with the variant's sprite

* reformat

* added data in error message

* added read comfort + detection of missing json for existing variant

* fix an error of message display

* fix fetch color swap, missing a return

src/field/pokemon.ts

@@ -336,7 +336,7 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
                           console.error(`Could not load ${res.url}!`);
                           return;
                         }
-                        res.json()
+                        return res.json()
                       }).then(c => {
                           variantColorCache[key] = c;
                           resolve();