Fix a crash in the sprite editor of a child-object (4ian#6266)

Author: D8H

newIDE/app/src/ObjectEditor/Editors/SpriteEditor/SpritesList.js

@@ -628,6 +628,8 @@ const SpritesList = ({
             onClick={() => {
               onAddSprite(resourceSources[0]);
             }}
+            // The event-based object editor gives an empty list.
+            disabled={resourceSources.length === 0}
             label={<Trans>Add a sprite</Trans>}
             icon={<Add />}
             primary

newIDE/app/src/ObjectEditor/Editors/SpriteEditor/index.js

@@ -672,7 +672,9 @@ export default function SpriteEditor({
     <I18n>
       {({ i18n }) => (
         <>
-          {spriteConfiguration.getAnimationsCount() === 0 ? (
+          {spriteConfiguration.getAnimationsCount() === 0 &&
+          // The event-based object editor gives an empty list.
+          imageResourceExternalEditors.length > 0 ? (
             <Column noMargin expand justifyContent="center">
               <EmptyPlaceholder
                 title={<Trans>Add your first animation</Trans>}
@@ -691,16 +693,9 @@ export default function SpriteEditor({
                 onAction={() => {
                   importImages();
                 }}
-                onSecondaryAction={
-                  imageResourceExternalEditors.length
-                    ? () => {
-                        createAnimationWith(
-                          i18n,
-                          imageResourceExternalEditors[0]
-                        );
-                      }
-                    : undefined
-                }
+                onSecondaryAction={() => {
+                  createAnimationWith(i18n, imageResourceExternalEditors[0]);
+                }}
               />
             </Column>
           ) : (