move SMART error handling into get_disks

because we never ever want to die in get_disks because of a
single disk, but the nodes/xyz/disks/smart API path is
allowed to fail if a disk device is unsupported by smartctl
or something else goes wrong.

PVE/API2/Disks.pm

@@ -138,6 +138,8 @@ __PACKAGE__->register_method ({
 	    $result = PVE::Diskmanage::get_smart_data($disk);
 	}
 
+	$result->{health} = 'UNKOWN' if !defined $result->{health};
+
 	return $result;
     }});