Empty source strings should not be stored

@podarok: I think you might experience a different bug. Our bug here is that the SOURCE string is empty, while on your screenshot, none of the source strings are empty.

@claudiu.cristea: IMHO, first we should check in potx itself. I'd imagine we need to solve this in the "save string callback" functions, one of which is implemented in potx and another one is implemented in l10n_server. We should IMHO store an error for these strings as well, so the warning report will include these bogus sources.

@podarok: Yes, that IMHO should be a new issue.

Opened a sister issue for potx at #609590: Do not store empty strings, signal an error instead which has the potx specific fixes. We need to use the same empty string treatment here, and I've added test coverage for that as well to ensure we have this right. Actually committing this, but don't know the exact time when I can roll this out (not now).

Best would be to also add an update function to convert empty source strings to warnings (since we know the file name and line info for them, we can easily generate these error messages on an update). And then remove these strings. That would help all kinds of sites running this module to update properly instead of just a one-off hackish rollout on localize.drupal.org.

Making needs work on that, but committed the attached patch, so even if this rolls out, such future modules will mark errors.

I've did manual update on deployment on drupal.org, did not add update function since this should not be a significant problem for other users most probably. Consider it done.

@hass: read #7 up there please.