fix: Provide a reasonable well-known fallback

If the well-known look fails (not json, 404, etc.) we should assume a
reasonable fallback (domain part with https prepended). As clients are
expected to call Client.checkHomeserver on the resulting domain anyways
we can safely assume this default, as it is still validated, if there
is actually a matrix homeserver running on that endpoint.

lib/src/client.dart

@@ -296,16 +296,26 @@ class Client extends MatrixApi {
   Future<WellKnownInformation> getWellKnownInformationsByUserId(
     String MatrixIdOrDomain,
   ) async {
-    final response = await http
-        .get(Uri.https(MatrixIdOrDomain.domain, '/.well-known/matrix/client'));
-    var respBody = response.body;
     try {
-      respBody = utf8.decode(response.bodyBytes);
+      final response = await http.get(
+          Uri.https(MatrixIdOrDomain.domain, '/.well-known/matrix/client'));
+      var respBody = response.body;
+      try {
+        respBody = utf8.decode(response.bodyBytes);
+      } catch (_) {
+        // No-OP
+      }
+      final rawJson = json.decode(respBody);
+      return WellKnownInformation.fromJson(rawJson);
     } catch (_) {
-      // No-OP
+      // we got an error processing or fetching the well-known information, let's
+      // provide a reasonable fallback.
+      return WellKnownInformation.fromJson(<String, dynamic>{
+        'm.homeserver': <String, dynamic>{
+          'base_url': Uri.https(MatrixIdOrDomain.domain, '').toString(),
+        },
+      });
     }
-    final rawJson = json.decode(respBody);
-    return WellKnownInformation.fromJson(rawJson);
   }
 
   @Deprecated('Use [checkHomeserver] instead.')