Connection problems (or intermittent errors) stop chain_builds

[berolinux]

Using abf chain_build on a long list of packages (e.g. an update of all KDE packages) frequently results in e.g.

345217 (openmandriva/qt5-qtbase:x86_64 - build started)
Internal server error: it has returned non-json data. 

where the "Internal server error" is a temporary connection problem or a temporary server outage (e.g. timeout).
At that point, the chain_build stops and is hard to resume (edit the file list to remove all items that have already been built; make sure everything that was in the queue at the same time finished successfully, ...)

It would be nice to retry instead of aborting the entire chain_build at a problem that probably is none.