If dump doesn't generate data into some image file the respective file
is not created at all as it used to be in 1.5. This brings potential
problem -- if the file with the image name exists during dump (e.g. a
dump file left from previous, maybe unsuccessful, dump) then restore
would pick this file and read bad/wrong/fake data from it.

To return the proper behavior back the file with the name of empty image
should be removed.

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>