Fix 5024 - diagnostic on unresolved catch types, added test case

lib/compiler/implementation/resolver.dart

Index: lib/compiler/implementation/resolver.dart
diff --git a/lib/compiler/implementation/resolver.dart b/lib/compiler/implementation/resolver.dart
index 166b55204697de309d707b38821740336f1f8ef6..9bec4367defffc025f59fb2bb033cacec06e826a 100644
--- a/lib/compiler/implementation/resolver.dart
+++ b/lib/compiler/implementation/resolver.dart
@@ -1936,7 +1936,10 @@ class ResolverVisitor extends CommonResolverVisitor<Element> {
     }
 
     Scope blockScope = new BlockScope(scope);
+    var wasTypeRequired = typeRequired;
+    typeRequired = true;
     doInCheckContext(() => visitIn(node.type, blockScope));
+    typeRequired = wasTypeRequired;
     visitIn(node.formals, blockScope);
     visitIn(node.block, blockScope);
   }