10l: Ignore error output from failed attempt to read snapshot_version.

Originally committed as revision 17578 to svn://svn.ffmpeg.org/ffmpeg/trunk

version.sh

 #!/bin/sh
 
 # check for SVN revision number
-revision=$(cat snapshot_version)
+revision=$(cat snapshot_version 2> /dev/null)
 test $revision || revision=$(cd "$1" && LC_ALL=C svn info 2> /dev/null | grep Revision | cut -d' ' -f2)
 test $revision || revision=$(cd "$1" && grep revision .svn/entries 2>/dev/null | cut -d '"' -f2)
 test $revision || revision=$(cd "$1" && sed -n -e '/^dir$/{n;p;q}' .svn/entries 2>/dev/null)