#32 Bad handling of pre-1.7 .pdz files

[Kai Runte]

As mentioned in a different bug ("[ 1104022 ] Pedro
Version 1.6 and version 1.7 are not consistent"), Pedro
1.7+ is not able to load file from Pedro 1.6 and below.
The problem is that it doesn't create any error
message, but silently tries to load the file and fails
(silently).
There should be an error message stating that the file
the user select is from an incompatible version.