XimeaCamera._fetch_data: avoid calling xiapi.Image.get_image_data_numpy twice

We already have done the conversion of the data in the Image object to
numpy once, so don't do it twice.

Author: carandraug

microscope/cameras/ximea.py

@@ -59,7 +59,7 @@ def _fetch_data(self):
             _logger.info('Sending image')
             if trigger_type == 'XI_TRG_SOFTWARE':
                 self._triggered = False
-            return self.img.get_image_data_numpy()
+            return data
         except Exception as err:
             if getattr(err, 'status', None) == 10:
                 # This is a Timeout error