nsis: Make sure the registry keys exist
It was reported on nasm forum (http://forum.nasm.us/index.php?topic=1013.0)
that if uninstallation procedure get stopped (for any reason) in a middle
leading to read empty registry values an attempt to remove arbitrary
files might happen. So make sure there are some sane values in registry.
N.B: People, if you find some bug in nasm, don't write to forum, file
bug directly in bugzilla, if it's not a bug we simply close it, otherwise
we might miss serious problems like this one!
Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>