[Feature Request]: Make it so that a failed generation attempt doesn't remove "continue" timestring

### Is there an existing issue for this?

- [X] I have searched the existing issues and checked the recent builds/commits

### What would your feature do ?

Make it so that a failed generation attempt doesn't remove "continue" timestring

### Proposed workflow

1. Attempt to generate frames
2. Fails due to incorrect formatting of prompt or frame data
3. Continue timestring doesn't get blanked out

### Additional information

_No response_

### Are you going to help adding it?

No

No file, test, or entry point is identified. Start by tracing the frame-generation workflow and the handling of the "continue" timestring after invalid prompt or frame data causes a failure. Done means a failed attempt leaves the timestring unchanged; verify this with a reproducible invalid-input run or the relevant generation test.

Written by the indexing model from the issue text.