fix: GenAI - Fixed response validation error during streaming

Previously, when the response was blocked by safety, the exception was non-informative.

PiperOrigin-RevId: 622291778

vertexai/generative_models/_generative_models.py

@@ -1022,17 +1022,17 @@ def _send_message_streaming(
         full_response = None
         for chunk in stream:
             chunks.append(chunk)
-            if full_response:
-                _append_response(full_response, chunk)
-            else:
-                full_response = chunk
             # By default we're not adding incomplete interactions to history.
             if self._response_validator is not None:
                 self._response_validator(
                     response=chunk,
                     request_contents=request_history,
                     response_chunks=chunks,
                 )
+            if full_response:
+                _append_response(full_response, chunk)
+            else:
+                full_response = chunk
             yield chunk
         if not full_response:
             return
@@ -1089,18 +1089,17 @@ async def async_generator():
             full_response = None
             async for chunk in stream:
                 chunks.append(chunk)
-                if full_response:
-                    _append_response(full_response, chunk)
-                else:
-                    full_response = chunk
                 # By default we're not adding incomplete interactions to history.
                 if self._response_validator is not None:
                     self._response_validator(
                         response=chunk,
                         request_contents=request_history,
                         response_chunks=chunks,
                     )
-
+                if full_response:
+                    _append_response(full_response, chunk)
+                else:
+                    full_response = chunk
                 yield chunk
             if not full_response:
                 return