catch 500 error and return to users when using `fast` strategy for images

[yuming-long]

Describe the bug We don't support any fallback for fast strategy on images anymore, and unst will raise value error if partition uses fast strategy for image files. We should catch this 500 error, raise a 400 HTTPException with corresponding error message.

To Reproduce

• make install

• make run-web-app

• Filetype: image

• Any additional API parameters: fast strategy