Pointer assertions for substring
diff --git a/tinyxml2.h b/tinyxml2.h
index 332e124..6468e16 100755
--- a/tinyxml2.h
+++ b/tinyxml2.h
@@ -139,6 +139,8 @@
     ~StrPair();

 

     void Set( char* start, char* end, int flags ) {

+        TIXMLASSERT( start );

+        TIXMLASSERT( end );

         Reset();

         _start  = start;

         _end    = end;