altosui: Catch errors opening USB devices. Limit list to relevant devices

Avoids a segfault when failing to open a device. Limit listed telemetry
devices to just TeleDongle units.

Signed-off-by: Keith Packard <keithp@keithp.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/ao-tools/altosui/AltosDeviceDialog.java b/ao-tools/altosui/AltosDeviceDialog.java
index eb70877c..08921c3d 100644
--- a/ao-tools/altosui/AltosDeviceDialog.java
+++ b/ao-tools/altosui/AltosDeviceDialog.java
@@ -41,6 +41,10 @@ public class AltosDeviceDialog {
 							       devices[0]);
 			return (altos_device) o;
 		} else {
+			JOptionPane.showMessageDialog(frame,
+						      "No AltOS devices available",
+						      "No AltOS devices",
+						      JOptionPane.ERROR_MESSAGE);
 			return null;
 		}
 	}