Quick fix for InspIRCD dns.cpp until someone fixes it

diff -ruN inspircd-inspircd.orig/src/dns.cpp inspircd-inspircd/src/dns.cpp
--- inspircd-inspircd.orig/src/dns.cpp  2011-06-24 01:21:01.000000000 +0000
+++ inspircd-inspircd/src/dns.cpp       2012-03-20 19:04:33.687154936 +0000
@@ -795,7 +795,7 @@
                case DNS_QUERY_PTR:
                        o = 0;
                        q = 0;
-                       while (q == 0 && i < length && o + 256 < 1023)
+                       while (q == 0 && i >= 0 && i < length && o + 256 < 511)
                        {
                                if (header.payload[i] > 63)
                                {