qemublocktest: Add 'empty' case for checkpoint bitmap handling

Signed-off-by: NPeter Krempa <pkrempa@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>

tests/qemublocktest.c

@@ -1430,6 +1430,8 @@ mymain(void)
         ret = -1; \
     } while (0)
 
+    TEST_BITMAP_BLOCKCOMMIT("empty", 1, 2, "empty");
+
     TEST_BITMAP_BLOCKCOMMIT("basic-1-2", 1, 2, "basic");
     TEST_BITMAP_BLOCKCOMMIT("basic-1-3", 1, 3, "basic");
     TEST_BITMAP_BLOCKCOMMIT("basic-2-3", 2, 3, "basic");

tests/qemublocktestdata/bitmapblockcommit/empty

+pre job bitmap disable:
+merge bitmpas: