Cleanup before throwing RuntimeError

[laggykiller]

Currently, liq_result_p, liq_image, liq_attr are not cleaned if RuntimeError occurs.

This can potentially cause memory leak, such as in the following example:

import imagequant
from PIL import Image

def smallest_quant(image: Image) -> Image:
    image_quant = None
    for i in range(11, 101, 5):
        try:
            image_quant = imagequant.quantize_pil_image(  # type: ignore
                image,
                dithering_level=1.0,
                max_colors=256,
                min_quality=0,
                max_quality=i,
            )
            return image_quant
        except RuntimeError:
            pass

    return image

This PR cleans up liq_result_p, liq_image, liq_attr before throwing RuntimeError.

[flozz]

Oops, nice catch! :)

[flozz]

Released in v1.1.4, packages build in progress.

Thank you! :)