bar_cmd_font: fix leak of font
bar_cmd_font: fix leak of font

join_args is a freshly allocated string and can be used as is.

Found through static analysis.

taiyu-len/sway,ascent12/sway,ascent12/sway,1ace/sway,taiyu-len/sway,ascent12/sway,SirCmpwn/sway,1ace/sway,1ace/sway,taiyu-len/sway