Description:
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The SVN module http://pecl.php.net/package/svn  calls svn_utf_cstring_to_utf8 to 
convert string to utf-8 encoding without checking the return value of 
svn_utf_cstring_to_utf8.  
When svn_utf_cstring_to_utf8 failed, the *dist pointer will be NULL. Thus the 
following call to svn_path_canonicalize would lead to a segfault.

Test script:
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Call functions like svn_fs_is_file with a GBK encoding filename will cause segfault.