Fixed bug when binary file changed in RCS.

Fixed bug when binary file changed in RCS.

If the RCS file being tracked is missing a final new-line character, the
program would crash whenever the last line was deleted and then added.

Reproduction steps:

mkdir /tmp/bug_demo && cd /tmp/bug_demo
rcs -i foo.txt
echo -n "foo" > foo.txt
ci foo.txt
co -l foo.txt
echo -n "d" >> foo.txt
ci foo.txt
git init
~/bin/rcs-fast-export.rb foo.txt,v