libutil properties_read() bug: patch for review

[Antony Mawer]

Hi,

I recently hit upon a bug in sysinstall, getting an "Invalid realloc 
size of 0" error that caused sysinstall to terminate. I eventually 
tracked it down to a bug in the properties_read() function of libutil, 
which occurs only when reading a properties file of 4096 bytes or 
greater. This is because libutil discards its current state when the 
buffer runs out (4096 bytes) and it must refill the buffer, causing the 
properties file (*.inf) to be incorrectly read.

I've made a patch that's attached to the PR I filed, PR 89181, but was 
hoping to get some extra eyes on the patch to make sure that there's 
nothing amiss with the patch:

     http://www.freebsd.org/cgi/query-pr.cgi?pr=89181

Hopefully someone can review this and see about getting it committed for 
6.1!

-Antony