Post multipart fixes

Couple of fixes based on valgrind reports after multipart merge.
I removed a check for tasks_finished from task_callback() because it took a shortcut and stopped the loop without properly freeing stuff.

I'm also not completely sure about the 'state' approach with server's io_channel. At the moment I have no idea why recipe_handler() returns FALSE when switching to RECIPE_RUNNING state resulting in 2 calls to recipe_handler_finish() callback.