pb2py: properly handle nested messages and enums

protob/pb2py

@@ -116,6 +116,8 @@ class Descriptor:
         for file in self.files:
             self.messages += file.message_type
             self.enums += file.enum_type
+            for message in file.message_type:
+                self._nested_types_from_message(message)
 
         if not self.messages and not self.enums:
             raise RuntimeError("No messages and no enums found.")
@@ -125,6 +127,12 @@ class Descriptor:
 
         self.out_dir = None
 
+    def _nested_types_from_message(self, message):
+        self.messages += message.nested_type
+        self.enums += message.enum_type
+        for nested in message.nested_type:
+            self._nested_types_from_message(nested)
+
     def find_message_types(self, message_type):
         message_types = {}
         try: