Update bot.pl: in case of empty/not defined title, it won't crash

With this it will not give:
"Use of uninitialized value $title in string eq at bot.pl line 87, <GEN0> line 78." warning, but still will give:
"Use of uninitialized value $uri in concatenation (.) or string at /usr/local/share/perl/5.14.2/URI/Find.pm line 358, <GEN0> line 78.".
Merge pull request #2 from geohhot/patch-2

In case of empty/not defined title, it won't crash