Fix memory leak/Use BEGINS_WITH macro
Fix memory leak/Use BEGINS_WITH macro

The orignal proposed code had a memory leak when returning true.
Furthermore I included the handy BEGINS_WITH macro of i3 which makes the
code (IMHO) a lot more readable.

Dettorer/i3status,i3/i3status,Dettorer/i3status,jasperla/i3status,peder2tm/i3status-netdev,i3/i3status,flammi/i3status,lexszero/i3status,i3/i3status,jasperla/i3status,flammi/i3status,jasperla/i3status,lexszero/i3status,peder2tm/i3status-netdev,i3/i3status,lexszero/i3status,lexszero/i3status,Gravemind/i3status,Gravemind/i3status,peder2tm/i3status-netdev,Dettorer/i3status,flammi/i3status,Dettorer/i3status,Gravemind/i3status,peder2tm/i3status-netdev,flammi/i3status,jasperla/i3status,Gravemind/i3status