qcow2: Catch bdrv_getlength() error

The call to bdrv_getlength() from qcow2_check_refcounts() may result in
an error. Check this and abort if necessary.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block/qcow2-refcount.c

diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
index d2cb6a8..e79895d 100644
--- a/block/qcow2-refcount.c
+++ b/block/qcow2-refcount.c
@@ -1487,6 +1487,11 @@
     int ret;
 
     size = bdrv_getlength(bs->file);
+    if (size < 0) {
+        res->check_errors++;
+        return size;
+    }
+
     nb_clusters = size_to_clusters(s, size);
     if (nb_clusters > INT_MAX) {
         res->check_errors++;