Resolve "memory corruption bugs in libsane"

This adds fixes for security issues pointed out in #279 (closed).

In 1.0.30 we opted to disable the epsonds backend's network autodiscovery to mitigate security issues because it does not support network scanners. The changes here were implemented before realizing that 🤦 but they are useful in case someone wants to have a go add making it work.

/cc @kevinbackhouse