MDL-51854 atto_image: Allow other plugins to handle drop events

The drop handler should only return false if it has actually handled the
drop event (i.e. it was an image) - otherwise, Atto plugins loaded after
this one don't get an opportunity to handle other drop events.

lib/editor/atto/plugins/image/yui/build/moodle-atto_image-button/moodle-atto_image-button-debug.js

@@ -333,8 +333,8 @@ Y.namespace('M.atto_image').Button = Y.Base.create('button', Y.M.editor_atto.Edi
             };
             xhr.open("POST", M.cfg.wwwroot + '/repository/repository_ajax.php?action=upload', true);
             xhr.send(formData);
+            return false;
         }
-        return false;
 
 },
 

lib/editor/atto/plugins/image/yui/build/moodle-atto_image-button/moodle-atto_image-button.js

@@ -333,8 +333,8 @@ Y.namespace('M.atto_image').Button = Y.Base.create('button', Y.M.editor_atto.Edi
             };
             xhr.open("POST", M.cfg.wwwroot + '/repository/repository_ajax.php?action=upload', true);
             xhr.send(formData);
+            return false;
         }
-        return false;
 
 },
 

lib/editor/atto/plugins/image/yui/src/button/js/button.js

@@ -331,8 +331,8 @@ Y.namespace('M.atto_image').Button = Y.Base.create('button', Y.M.editor_atto.Edi
             };
             xhr.open("POST", M.cfg.wwwroot + '/repository/repository_ajax.php?action=upload', true);
             xhr.send(formData);
+            return false;
         }
-        return false;
 
 },