Made sure that DRD processes empty address ranges without triggering an assertion failure. Added a unit test in drd/tests/unit_bitmap.c.

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@11346 a5019735-40e9-0310-863c-91ae7b9d1cf9
diff --git a/drd/tests/unit_bitmap.c b/drd/tests/unit_bitmap.c
index 280943c..236cf06 100644
--- a/drd/tests/unit_bitmap.c
+++ b/drd/tests/unit_bitmap.c
@@ -63,6 +63,7 @@
 static
 struct { Addr address; SizeT size; BmAccessTypeT access_type; }
   s_test1_args[] = {
+    {                           0, 0, eLoad  },
     {                           0, 1, eLoad  },
     {                         666, 4, eLoad  },
     {                         667, 2, eStore },