[PATCH] JavaHL: Fix return value from the java svn_stream_t read function to be compatible with the txdelta_next_window function

Greetings,

While working on enhancements for JavaHL I ran into a problem
implementing svn_txdelta_apply
call because txdelta_next_window would segfault while trying to calculate
the streams checksum. I traced it down to code in the InputStream.cpp that
returns -1 when end of stream is reached. -1 does not work with
txdelta_next_window
because it expects 0 to indicate end of stream. Spot checking other svn
functions, that use streams, shows that they check for greater than 0
return value as indication that there is data to be process. Also as far
as I can tell apr_size_t maps to size_t, which implies that it is a signed
type making 0 more sensible than -1 as end of steam indicator.

[[[
    JavaHL: Fix return value from the java svn_stream_t read function to be
compatible with the txdelta_next_window function

    [ in subversion/bindings/javahl/native ]

    * InputStream.cpp
      (read): Return 0 instead of -1 as expected by the txdelta_next_window
function
]]]

Thank you,

Vladimir