ensure additional args are a dict

They should already be templated before hitting this point?
otherwise the class needs the task variables passed into it.
relates to #13518 and  https://groups.google.com/forum/#!msg/ansible-project/esoBcphHwHs/Ghgi_M-MCQAJ

lib/ansible/parsing/mod_args.py

@@ -137,6 +137,8 @@ class ModuleArgsParser:
         # than those which may be parsed/normalized next
         final_args = dict()
         if additional_args:
+            if not isinstance(additional_args,dict):
+                raise AnsibleParserError('Complex args should be a dictionary')
             final_args.update(additional_args)
 
         # how we normalize depends if we figured out what the module name is