Source read errors - assume zeros

[Evengard]

Sometimes when copying a block device, you stumble upon bad sectors. It could happen with any drive, and it could be as small as 1 sector on the whole drive.
Unfortunately, diskrsync just stops on read error.
Sometimes backing up whatever you can from that drive to a remote location is the only option - because you don't have enough space to run ddrescue locally.
Sure, I don't ask to implement ddrescue inside diskrsync. But it would be nice that on a read error, diskrsync just assumed the read returned all zeroes and kept transfering other data.
This mode may be non-default and be enabled with some kind of flag. Still, this would allow to preserve the rest of the data.