get_dbpedia_uris() does not fail gracefully if endpoint is not accessible

[ablaette]

As I have started to process increasingly large corpora (using a local docker container with DBpedia Spotlight), I encountered an ungraceful abort. As it seems, the container was temporarily not available.

I assume that the unavailability of the container was a temporary phenomenon. But get_dbpedia_uris() should be more robust in this scenario. The best way would be that get_dbpedia_uris() retrys and aborts graceful after a number of unsuccessful attempts.

[ablaette]

Addressed.