vbo: Fix vbo_split_copy to pass correct max_index to draw.

vbo_split_copy was passing one past the max_index to draw function
which caused _tnl_draw_prims function to read uninitialized values
from copied array.

Bug was spoted in valgrind report of progs/tests/cva_huge.

src/mesa/vbo/vbo_split_copy.c

@@ -196,7 +196,7 @@ flush( struct copy_context *copy )
 	       &copy->dstib,
 	       GL_TRUE,
 	       0,
-	       copy->dstbuf_nr );
+	       copy->dstbuf_nr - 1 );
 
    /* Reset all pointers: 
     */