Changeset : remote shooting (PTP): partial fix for cameras that can write JPEG files ...

remote shooting (PTP): partial fix for cameras that can write JPEG files in multiple passes but don't seek within the file
​http://chdk.setepontos.com/index.php?topic=4338.msg116487#msg116487
Affected models come from the DryOS r39..r49 generations. Initial CAM_FILEWRITETASK_MULTIPASS cameras: a3200, a490, a495.