swaybar: explicitly check return value of getdelim
swaybar: explicitly check return value of getdelim

This prevents an signed-to-unsigned conversion error on buffer_index if
getdelim fails and returns -1, which caused swaybar to try to search the
header for the array and immediately failing

1ace/sway,1ace/sway,ascent12/sway,1ace/sway,ascent12/sway,SirCmpwn/sway,ascent12/sway