Fix delta composer reading past EOF by making it stop reading after the first partial read.
Fix delta composer reading past EOF by making it stop reading after the first
partial read.

* subversion/libsvn_delta/text_delta.c
  (svn_txdelta_stream_t): Add a more_source field to indicate if we can read
   more from the source stream.
  (svn_txdelta_next_window): Stop reading from stream->source after a partial
   read has signalled EOF. Also, use the now-common SVN_ERR() macro to report
   errors to callers.

jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion