BUG/MEDIUM: resolvers: Really ignore trailing dot in domain names

BUG/MEDIUM: resolvers: Really ignore trailing dot in domain names

When a string is converted to a domain name label, the trailing dot must be
ignored. In resolv_str_to_dn_label(), there is a test to do so. However, the
trailing dot is not really ignored. The character itself is not copied but
the string index is still moved to the next char. Thus, this trailing dot is
counted in the length of the last encoded part of the domain name. Worst,
because the copy is skipped, a garbage character is included in the domain
name.

This patch should fix the issue #1528. It must be backported as far as 2.0.