message: objc: fix handling of std::vector<std::vector<T>> return type
diff: @@ -1123,7 +1123,7 @@ class ObjectiveCWrapperGenerator(object):
  if cpp_type.find("::") == -1:
  cpp_type = self.get_namespace_prefix(cpp_type) + cpp_type
  prologue.append("NSMutableArray<NSMutableArray<" + objc_type + ">*>* retVal = [NSMutableArray new];")
  - ret_val = "std::vector<" + cpp_type + "> retValVector = "
  + ret_val = "std::vector< std::vector<" + cpp_type + "> > retValVector = "
  epilogue.append("CV2OBJC2(" + cpp_type + ", " + objc_type[:-1] + ", retValVector, retVal);")
  elif ret_type.startswith("Ptr_"):
  cpp_type = type_dict[ret_type]["c_type"]
  