The cache support was recently overhauled to support generators, but

this caused the MissingChunkError to be propagated to the code iterating

through results, rather than the code initially fetching the data from

cache.
To fix this, I've split the function into two: One that does the initial

fetching and missing chunk detection, and one that iterates through

results.
A unit test was added that failed with a propagated MissingChunkError

before this fix, and succeeded in falling through to the cache data

generation function after the fix.

The new unit test failed before, and passed after. Also tested manually.