In component refactor, ensure consistency about trailing slashes

[jluethi]

An observation by @adrtsc

The reason is that the image component looks different between the two versions. In the multiplexing version, the component received by the task looks like this:
"300620234compoundAssaycycle0.zarr/D/16/0"
while for the non-multiplexing version, the component looks like this:
"300620234compoundAssaycycle0.zarr/D/16/0/"

Let's make sure we only store our image paths one way, also to avoid potential duplicates that actually refer to the same image

[tcompa]

Closing in favor of #677.