internal_links: Add Variable realmUrlWithSlash to add '/'

updates the URL construction to include a trailing slash
before the fragment identifier This ensures that the URL
is properly formatted and makes the url likified.
Fixes: #845

Author: satyam372

lib/model/internal_link.dart

@@ -59,7 +59,7 @@ String? decodeHashComponent(String str) {
 Uri narrowLink(PerAccountStore store, Narrow narrow, {int? nearMessageId}) {
   // TODO(server-7)
   final apiNarrow = resolveDmElements(
-    narrow.apiEncode(), store.connection.zulipFeatureLevel!);
+  narrow.apiEncode(), store.connection.zulipFeatureLevel!);
   final fragment = StringBuffer('narrow');
   for (ApiNarrowElement element in apiNarrow) {
     fragment.write('/');
@@ -95,8 +95,11 @@ Uri narrowLink(PerAccountStore store, Narrow narrow, {int? nearMessageId}) {
   if (nearMessageId != null) {
     fragment.write('/near/$nearMessageId');
   }
+  final realmUrlWithSlash = store.realmUrl.path.endsWith('/')
+      ? store.realmUrl
+      : store.realmUrl.replace(path: '${store.realmUrl.path}/');
 
-  return store.realmUrl.replace(fragment: fragment.toString());
+  return realmUrlWithSlash.replace(fragment: fragment.toString());
 }
 
 /// A [Narrow] from a given URL, on `store`'s realm.