check for bytes return type and dictifiy it

[d-v-b]

Fixes #707

self.fs.cat returns an instance of bytes if keys2 has one element, which causes an error when fsmap.getitems attempts to access the items property of that value. This PR checks if self.fs.cat returned an instance of bytes, and if so, sticks it in a dict. This kind of problem might be an argument for type annotations, which would have flagged this issue earlier.

[martindurant]

might be an argument for type annotations

I am not against it in principle, but where I've been forced to use it myself (pandas, xarray), it took far more effort to twist the type system to what I need, and several errors in that process. Perhaps my coding style is inherently type-unfriendly.

[martindurant]

I suppose it's worth a test?
NB: the s3fs failure is some intermittent conda problem.

[martindurant]

Can someone confirm that this fixes xarray? @keewis

[keewis]

it does! I can confirm that the xarray test fails with 2021.07.0 and passes with this branch

[martindurant]

Rerunning tests, will merge when green.

[martindurant]

Thank you @d-v-b . I still don't quite understand why this became an issue now, but never mind!

[jakirkham]

Would it be possible to tag a release with this change @martindurant ? 🙂 No worries if you are busy

[martindurant]

Waiting on #731