LGTM.com - false positive, python: Using a non-iterable as the object in a 'for' loop

**Description of the false positive**

The loop object is expected to be an iterable. The code actually calls `iter()` on it before the loop to enforce that. I'm not sure why the analysis thought it might not be.

https://lgtm.com/projects/g/snarfed/granary/snapshot/2029f12edb95da96a5f1b39ecfcce440c8d75dea/files/granary/jsonfeed.py#xb80999fcab2f40c8:1

maybe related to #1833? different repro though.

thanks for all your work on LGTM and QL, they're both great!