Description:
------------
Some svnserve server returns Zero-length error message like this.
  "( failure ( ( 170001 0: 56:C:\Projects\subversion-
1.4.4\subversion\svnserve\serve.c 443 ) ) )"
In that case, svn_info() function causes Segmentation fault. 

I modified source file "svn.c" to avoid this problem;
  
---- php_svn_handle_error() in svn.c ---
266  smart_str_appendl(&s, ") ", 2);
267  smart_str_appendl(&s, itr->message, strlen(itr->message));
268                 
----
---- modified code ---
266  smart_str_appendl(&s, ") ", 2);
267  if (itr->message) {
268    smart_str_appendl(&s, itr->message, strlen(itr->message));
269  } else {
270    smart_str_appendl(&s, "(null)", 6);
271  }


Test script:
---------------
$url = "svn://(svnserve server)/";
$username = "(username)";
$password = "(password)";
svn_auth_set_parameter(PHP_SVN_AUTH_PARAM_IGNORE_SSL_VERIFY_ERRORS, true);
svn_auth_set_parameter(SVN_AUTH_PARAM_NON_INTERACTIVE,              true);
svn_auth_set_parameter(SVN_AUTH_PARAM_NO_AUTH_CACHE,                true);
svn_auth_set_parameter(SVN_AUTH_PARAM_DONT_STORE_PASSWORDS,         true);

svn_auth_set_parameter(SVN_AUTH_PARAM_DEFAULT_USERNAME, "$username");
svn_auth_set_parameter(SVN_AUTH_PARAM_DEFAULT_PASSWORD, "$password");

$svn_info = svn_info($url, false, SVN_REVISION_HEAD);
var_dump($svn_info);


Expected result:
----------------
Warning is reported like this;
Warning: svn_info(): svn error(s) occured
170001 (Authorization failed) (Could not get message)


Actual result:
--------------
Segmentation fault