refactor(backend): fixed default storage call

lib/Ravada/Domain.pm

@@ -266,7 +266,7 @@ sub _set_vm($self, $vm, $force=0) {
 sub _check_equal_storage_pools($self, $vm2) {
     my $vm1 = $self->_vm;
     my @sp;
-    push @sp,($vm1->default_storage_pool_name)  if $vm1->default_storage_pool;
+    push @sp,($vm1->default_storage_pool_name)  if $vm1->default_storage_pool_name;
     push @sp,($vm1->base_storage_pool)  if $vm1->base_storage_pool;
     push @sp,($vm1->clone_storage_pool) if $vm1->clone_storage_pool;