Image not update(in database image update blank value)

[eluser]Rocky Mehta[/eluser]
Your code getting me to display my error but not update my field if i am not change the chair_image field update a blank in to database.
if i am change the field(chair_image) it's working properly but if i m not change that field(chair_image) it's update a blank entry in to my database.
my error display is => You did not select a file to upload.