Merge branch 'jb36919' into 'master'

[bluez] Check for a null usableAdapter in bluez plugin. Fixes JB#36919

When the manager no longer has a usable adapter, usableAdapterChanged()
is emitted with a null adapter.

See merge request !10

src/bluez/provider_bluez.cpp

@@ -72,10 +72,17 @@ void Bridge::init()
 
 void Bridge::usableAdapterChanged(BluezQt::AdapterPtr adapter)
 {
-    qDebug() << "Found default bluetooth adapter" << adapter->ubi();
-
     adapter_ = adapter;
 
+    if (adapter.isNull()) {
+        static_cast<BlueZ*>(target_)->reset_properties();
+        devices_.clear();
+        connected_.clear();
+        return;
+    }
+
+    qDebug() << "Found default bluetooth adapter" << adapter->ubi();
+
     connect(adapter_.data(), &BluezQt::Adapter::poweredChanged
             , [this](bool powered) {
                 updateProperty("Powered", powered);