Truncate wm_name utf8 strings to first zero byte
Truncate wm_name utf8 strings to first zero byte

Fixes #3515

i3/i3,i3/i3,Airblader/i3,i3/i3,Airblader/i3-original,stapelberg/i3,stapelberg/i3,Airblader/i3,Airblader/i3-original,Airblader/i3-original,Airblader/i3,Airblader/i3-original,Airblader/i3,stapelberg/i3,i3/i3,stapelberg/i3,Airblader/i3-original