uru4000: Call irq stop handler immediately if the transfer is cancelled

The irq handler may already be stopped if stop_irq_handler is called. In
that case, we should immediately call the handler rather than just never
calling it.

This fixes deactivation when the device is unexpectedly unplugged.

Closes: #355

libfprint/drivers/uru4000.c

@@ -375,6 +375,10 @@ stop_irq_handler (FpImageDevice *dev, irqs_stopped_cb_fn cb)
       g_cancellable_cancel (self->irq_cancellable);
       self->irqs_stopped_cb = cb;
     }
+  else
+    {
+      cb (dev);
+    }
 }
 
 /***** STATE CHANGING *****/