SCAPE: only write the position list when saving images during the acuisition

[bls337]

position_list.pos was being written to the save directory whenever multiple positions were in use, regardless of whether "save images during acquisition" was checked. The acq_settings.json write right above it already respected that checkbox, this one didn't, so leaving "save images" unchecked with multiple positions configured still silently created a save directory containing just a stray position_list.pos file.

Change

AcquisitionEngineScape.java: added isSavingImagesDuringAcquisition() to the condition to prevent the position-list write, matching the existing acq_settings.json check.

// write the position list if we are using multiple positions
if (model_.acquisitions().settings().isSavingImagesDuringAcquisition()
        && model_.acquisitions().settings().isUsingMultiplePositions()) {