migration: Check that migration is active before cancel it

Signed-off-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Anthony Liguori <aliguori@us.ibm.com>
diff --git a/migration.c b/migration.c
index 7fd6c23..71b8aad 100644
--- a/migration.c
+++ b/migration.c
@@ -133,9 +133,9 @@
 {
     MigrationState *s = current_migration;
 
-    if (s)
+    if (s && s->get_status(s) == MIG_STATE_ACTIVE) {
         s->cancel(s);
-
+    }
     return 0;
 }