internal_link: Add tryResolveOnRealmUrl

Author: sirpengi

lib/model/internal_link.dart

@@ -78,3 +78,14 @@ Uri narrowLink(PerAccountStore store, Narrow narrow, {int? nearMessageId}) {
 
   return store.account.realmUrl.replace(fragment: fragment.toString());
 }
+
+/// Create a new `Uri` object in relation to a given realmUrl.
+///
+/// Returns `null` if `urlString` could not be parsed as a `Uri`.
+Uri? tryResolveOnRealmUrl(String urlString, Uri realmUrl) {
+  try {
+    return realmUrl.resolve(urlString);
+  } on FormatException {
+    return null;
+  }
+}

lib/widgets/content.dart

@@ -7,6 +7,7 @@ import '../api/core.dart';
 import '../api/model/model.dart';
 import '../model/binding.dart';
 import '../model/content.dart';
+import '../model/internal_link.dart';
 import '../model/store.dart';
 import 'code_block.dart';
 import 'dialog.dart';
@@ -661,12 +662,9 @@ void _launchUrl(BuildContext context, String urlString) async {
   }
 
   final store = PerAccountStoreWidget.of(context);
-  final Uri url;
-  try {
-    url = store.account.realmUrl.resolve(urlString);
-  } on FormatException { // TODO(log)
+  final url = tryResolveOnRealmUrl(urlString, store.account.realmUrl);
+  if (url == null) { // TODO(log)
     await showError(context, null);
-    if (!context.mounted) return; // TODO(dart): redundant for sake of lint
     return;
   }