allow api key empty when using ollama

the ollama API key is not required

webui/Main.py

@@ -734,7 +734,7 @@ if start_button:
         scroll_to_bottom()
         st.stop()
 
-    if llm_provider != "g4f" and not config.app.get(f"{llm_provider}_api_key", ""):
+    if llm_provider != "g4f" and llm_provider != 'ollama' and not config.app.get(f"{llm_provider}_api_key", ""):
         st.error(tr("Please Enter the LLM API Key"))
         scroll_to_bottom()
         st.stop()