avoid leaking data to HuggingFace (invoke-ai#2021)

Before making a concept download request to HuggingFace, the concepts
library module now checks the concept name against a downloaded list
of all the concepts currently known to HuggingFace.  If the requested
concept is not on the list, then no download request is made.

Author: lstein

ldm/invoke/concepts_lib.py

@@ -46,6 +46,9 @@ def get_concept_model_path(self, concept_name:str)->str:
         the named concept. Returns None if invalid or cannot
         be downloaded.
         '''
+        if not concept_name in self.list_concepts():
+            print(f'This concept is not known to the Hugging Face library. Generation will continue without the concept.')
+            return None
         return self.get_concept_file(concept_name.lower(),'learned_embeds.bin')
 
     def concept_to_trigger(self, concept_name:str)->str: