Fix error message for image access. (#3936)

### What problem does this PR solve?

#3883

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

api/apps/document_app.py

@@ -498,6 +498,9 @@ def change_parser():
 # @login_required
 def get_image(image_id):
     try:
+        arr = image_id.split("-")
+        if len(arr) != 2:
+            return get_data_error_result(message="Image not found.")
         bkt, nm = image_id.split("-")
         response = flask.make_response(STORAGE_IMPL.get(bkt, nm))
         response.headers.set('Content-Type', 'image/JPEG')

api/db/services/canvas_service.py

@@ -16,7 +16,7 @@
 import json
 from uuid import uuid4
 from agent.canvas import Canvas
-from api.db.db_models import DB, CanvasTemplate, UserCanvas
+from api.db.db_models import DB, CanvasTemplate, UserCanvas, API4Conversation
 from api.db.services.api_service import API4ConversationService
 from api.db.services.common_service import CommonService
 from api.db.services.conversation_service import structure_answer
@@ -65,16 +65,16 @@ def completion(tenant_id, agent_id, question, session_id=None, stream=True, **kw
             "id": session_id,
             "dialog_id": cvs.id,
             "user_id": kwargs.get("user_id", ""),
-            "message": [{"role": "assistant", "content": canvas.get_prologue()}],
             "source": "agent",
             "dsl": json.loads(cvs.dsl)
         }
         API4ConversationService.save(**conv)
+        if canvas.get_preset_param():
             yield "data:" + json.dumps({"code": 0,
                                     "message": "",
                                     "data": {
                                         "session_id": session_id,
-                                        "answer": canvas.get_prologue(),
+                                        "answer": "",
                                         "reference": [],
                                         "param": canvas.get_preset_param()
                                       }
@@ -82,6 +82,7 @@ def completion(tenant_id, agent_id, question, session_id=None, stream=True, **kw
                                    ensure_ascii=False) + "\n\n"
             yield "data:" + json.dumps({"code": 0, "message": "", "data": True}, ensure_ascii=False) + "\n\n"
             return
+        conv = API4Conversation(**conv)
     else:
         session_id = session_id
         e, conv = API4ConversationService.get_by_id(session_id)

api/db/services/conversation_service.py

@@ -47,6 +47,8 @@ class ConversationService(CommonService):
 
 def structure_answer(conv, ans, message_id, session_id):
     reference = ans["reference"]
+    if not isinstance(reference, dict):
+        reference = {}
     temp_reference = deepcopy(ans["reference"])
     if not conv.reference:
         conv.reference.append(temp_reference)