exec: fix memory leak in display of process output

ChangeLog.adoc

@@ -26,6 +26,7 @@ New features::
   * core: add option "time" in command /debug
   * api: add info "uptime" (WeeChat uptime)
   * api: add info "pid" (WeeChat PID) (issue #850)
+  * exec: fix memory leak in display of process output
   * fifo: add file fifo.conf and option fifo.file.path to customize FIFO pipe path/filename (issue #850)
   * irc: add server option "usermode" (issue #377, issue #820)
   * irc: add tag "self_msg" on self messages (issue #840)

src/plugins/exec/exec.c

@@ -340,6 +340,8 @@ exec_display_line (struct t_exec_cmd *exec_cmd, struct t_gui_buffer *buffer,
                 line_color);
         }
     }
+
+    free (line_color);
 }
 
 /*