Mismapped buttons for CanoScan LiDE 300
The Pixma MP150 backend assumes that all LiDE models have five front panel buttons, Start PDF Finish PDF Auto Scan Copy and Send. However this assumption is incorrect, LiDE 300 only has four, it's missing the Finish PDF button. And by chance the backend maps PIXMA_EV_BUTTON2 to this missing button.
This results in an issue where you cannot cancel batch scans using LiDE 300.
Would it be possible to map Button 2 for example to the Send button? That exists on both LiDE 300 and 400.
