We use NODISPLAY rendering somewhere in the code to test if the ps is valid.
That cause this:

Aha, NODISPLAY is really an explanation!  My bet is that with
that option 'pathbox' operator in snowflak.ps gives small enough
values for 'pagewidth' and/or 'pageheight' to end up below 'minsize'.
Therefore 'inwidth' or 'inheight' are set to zero and you are trying
to do a division by zero when calculating 'boxsize'.

If you will change in snowflak.ps these two definitions as follows:

/inwidth pagewidth minsize lt
     {1}{pagewidth minsize div} ifelse def
/inheight pageheight minsize lt
     {1}{ pageheight minsize div} ifelse def

then a resulting file is displayable by 'evince'.  No problems
with "%!" marker.

Original Red Hat bug:
https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=150722