[sudo-workers] execve() failure & closefrom() in fork_cmnd()

[Daniel Kopecek]

Hello,
  it seems that the usage of closefrom() in the fork_cmnd() function 
(http://www.sudo.ws/repos/sudo/file/ec0f2beaad36/src/exec.c#l140) should 
take into consideration that the execve() call might fail and ensure 
that the sv[1] descriptor used for sending the cstat structure back to 
the parent process stays open. In the current state and with 
def_closefrom not set to some higher number than sv[1], the descriptor 
gets closed and sudo doesn't report an error.

Proposed change:

    closefrom(def_closefrom < sv[1] ? sv[1] + 1 : def_closefrom);

Thanks,
Dan K.