gui: Don't show more than the 64 working channels in moninj

Previously, you could irreversibly set the override since
the gateware part would accept commands for the higher channels,
but of coure not report back the results.

See GitHub #601.

Signed-off-by: David Nadlinger <code@klickverbot.at>

artiq/dashboard/moninj.py

@@ -207,6 +207,10 @@ class _DeviceManager:
                 widget = None
                 if v["module"] == "artiq.coredevice.ttl":
                     channel = v["arguments"]["channel"]
+                    if channel > 63:
+                        # The moninj protocol is limited to 64 channels; ignore
+                        # any beyond that for now to avoid confusion.
+                        return
                     force_out = v["class"] == "TTLOut"
                     widget = _TTLWidget(
                         channel, self.send_to_device, force_out, k)