[xml] xmlNodeDumpOutputInternal segfault when usingt '/' as xpath expr

[Joel McConaughy <joel displayware com>]

I get the following segfault when using '/' as an xpath expression:

   Program received signal SIGSEGV, Segmentation fault.
   [Switching to Thread 1024 (LWP 6946)]
   0x400d5cb8 in xmlNodeDumpOutputInternal (ctxt=0xbffff640, cur=0x804d438)
       at xmlsave.c:737
   737        if ((cur->ns != NULL) && (cur->ns->prefix != NULL)) {

I have modified the xpath2.c sample to dump the results of an xpath 
expression using xmlNodeDumpOutput.  The problem can be reproduced by 
creating an input file containing '<a>1</a>' and passing the xpath 
expression '/'.  Every other xpath expression seems to work fine 
including malformed expressions.  I didn't find anything like this in 
the archive or bugzilla.

The only change I made to the sample was to replace update_xpath_nodes() 
with get_xpath_nodes().  The code is pretty simple and I can't see any 
problems however pilot error is always a possibility.  Help would be 
greatly appreciated.  Thanks.

Joel

libxml2-2.6.10 built from source using gcc 2.95.4
Debian 2.4.22

Here's the code:

/**