fix external id editing conditions (#2528)

* fix external id editing conditions

* fix typo

Author: CollinBeczak

src/components/AdminPane/Manage/ManageChallenges/EditChallenge/Messages.js

@@ -659,7 +659,7 @@ will not be able to make sense of it.
   disableOsmIdProperty: {
     id: "Admin.EditChallenge.form.disableOsmIdProperty",
     defaultMessage:
-      "This ID cannot be edited after challenge creation, this is to prevent task duplication. [Learn more](https://learn.maproulette.org/documentation/setting-external-task-identifiers/).",
+      "This ID cannot be edited after a challenge has successfully created tasks, this is to prevent task duplication. [Learn more](https://learn.maproulette.org/documentation/setting-external-task-identifiers/).",
   },
 
   customTaskStyleLabel: {

src/components/AdminPane/Manage/ManageChallenges/EditChallenge/Schemas/PropertiesSchema.js

@@ -54,7 +54,7 @@ export const jsSchema = (intl, user, challengeData) => {
  * > proper markup
  */
 export const uiSchema = (intl, user, challengeData, extraErrors, options = {}) => {
-  const sourceReadOnly = AsEditableChallenge(challengeData);
+  const sourceReadOnly = !AsEditableChallenge(challengeData).hasZeroTasks();
   const isCollapsed = options.longForm && (options.collapsedGroups || []).indexOf(STEP_ID) === -1;
   const toggleCollapsed =
     options.longForm && options.toggleCollapsed