fix to handle state.db being intied properly in process_pdf function

app.py

@@ -54,9 +54,12 @@ class PDFChatbot:
                 shutil.rmtree(self.state.vector_store_path)
             gr.Error(f"An error occurred: {str(e)}")
 
+    def is_db_ready(self):
+        return self.state.db is not None
+
     def chat_with_pdf(self, message, history):
-        if not self.state.is_db_ready():
-            yield "Please upload a PDF first to begin the conversation."
+        if not self.is_db_ready():
+            yield "Error: Database not ready."
             return
 
         retriever = self.state.db.as_retriever()