Fixed Bug #5492 "set @@session.read_rnd_buffer_size=33554432"

   crashes server on query

incremented size of allocated buffer in the init_rr_cache(sql/records.cc)
(
We are going to read the last three bytes of the buffer via uint3korr
This macro reads actually 4 bytes (for speed)
So, we have to allocate one more byte at the end of the buffer 
to avoid memory assertion fault
)

sql/records.cc

@@ -249,9 +249,15 @@ static int init_rr_cache(READ_RECORD *info)
   rec_cache_size=info->cache_records*info->reclength;
   info->rec_cache_size=info->cache_records*info->ref_length;
 
+  /*
+      We are going to read the last three bytes of the buffer via uint3korr
+      This macro reads actually 4 bytes (for speed)
+      So, we have to allocate one more byte at the end of the buffer 
+      to avoid memory assertion fault 
+  */
   if (info->cache_records <= 2 ||
       !(info->cache=(byte*) my_malloc_lock(rec_cache_size+info->cache_records*
-					   info->struct_length,
+					   info->struct_length+1,
 					   MYF(0))))
     DBUG_RETURN(1);
 #ifdef HAVE_purify