Add missing callback()

src/apps.js

@@ -648,6 +648,8 @@ function scheduleTask(appId, installationState, taskId, callback) {
                 appdb.update(appId, { installationState: exports.ISTATE_ERROR, error: boxError.toPlainObject(), taskId: null }, callback);
             } else if (!(installationState === exports.ISTATE_PENDING_UNINSTALL && !error)) { // clear out taskId except for successful uninstall
                 appdb.update(appId, { taskId: null }, callback);
+            } else {
+                callback();
             }
         });
     });