Fixed passing non-integers into preview window params

from openflexure_microscope.api.v1.views import MicroscopeView

from flask import jsonify, request

import logging

class GPUPreviewAPI(MicroscopeView):

            payload = JsonPayload(request)

            window = payload.param('window', default=[])

            fullscreen = False

            logging.debug(window)

            if len(window) != 4 or not all(isinstance(n, int) for n in window):

            if len(window) != 4:

                fullscreen = True

                window = None

            else:

              fullscreen = False

              window = [int(w) for w in window]

            self.microscope.camera.start_preview(fullscreen=fullscreen, window=window)

        elif operation == "stop":