irc/kvirc: unbreak with clang 4.0

src/modules/rijndael/libkvirijndael.cpp:331:11: error: ordered comparison between pointer and zero ('int *' and 'int')

if(len > 0)
   ~~~ ^ ~

src/modules/rijndael/libkvirijndael.cpp:357:11: error: ordered comparison between pointer and zero ('int *' and 'int')

if(len > 0)
   ~~~ ^ ~

Reported by: antoine (via exp-run)