Only set index available when errors are not ignored

Fixes an issue that occurs when flipping between sources before they finish loading. When that happens, the existing requests are cancelled, which causes their `catch` blocks to run asyncronously. This results in `setIndexActive` being called after `setIndexBusy` and a loading state that doesn't reflect the actual loading.

Fixes #12595

src/web/assets/cp/src/js/BaseElementIndex.js

@@ -463,8 +463,8 @@ Craft.BaseElementIndex = Garnish.Base.extend(
           this.selectDefaultSource();
         })
         .catch(() => {
-          this.setIndexAvailable();
           if (!this._ignoreFailedRequest) {
+            this.setIndexAvailable();
             Craft.cp.displayError(Craft.t('app', 'A server error occurred.'));
           }
         });
@@ -876,7 +876,7 @@ Craft.BaseElementIndex = Garnish.Base.extend(
     },
 
     updateElements: function (preservePagination, pageChanged) {
-      // Ignore if we're not fully initialized yet
+      // Ignore if we're not fully initialized yetjhh
       if (!this.initialized) {
         return;
       }
@@ -917,8 +917,8 @@ Craft.BaseElementIndex = Garnish.Base.extend(
           }
         })
         .catch((e) => {
-          this.setIndexAvailable();
           if (!this._ignoreFailedRequest) {
+            this.setIndexAvailable();
             Craft.cp.displayError(Craft.t('app', 'A server error occurred.'));
           }
         });