[Eric] Unhandled exception in performVersionCheck

[Davide Pesavento]

Hello,

as reported by a Gentoo user [1], there seems to be a bug in
performVersionCheck, where the code doesn't check for
self.__httpAlternatives being non-empty before accessing an element in
it. This happens when VersionsUrls is an empty list, as verified by
the reporter.

Regards,
Davide Pesavento

[1] https://bugs.gentoo.org/show_bug.cgi?id=303595