tablet: Ensure persistency of the outputName property

With this change, when the specified output is disconnected, it will
just behave as if none were selected but when it's connected again it
will pick it back up.

BUG: 456857

src/backends/libinput/connection.cpp

@@ -529,7 +529,7 @@ void Connection::applyScreenToDevice(Device *device)
 {
 #ifndef KWIN_BUILD_TESTING
     QMutexLocker locker(&m_mutex);
-    if (!device->isTouch()) {
+    if (!device->isTouch() && !device->isTabletTool()) {
         return;
     }
 
@@ -549,7 +549,7 @@ void Connection::applyScreenToDevice(Device *device)
             }
         }
     }
-    if (!deviceOutput) {
+    if (!deviceOutput && device->isTouch()) {
         // do we have an internal screen?
         Output *internalOutput = nullptr;
         for (Output *output : outputs) {

src/backends/libinput/device.cpp

@@ -628,8 +628,12 @@ void Device::setOrientation(Qt::ScreenOrientation orientation)
 void Device::setOutputName(const QString &name)
 {
 #ifndef KWIN_BUILD_TESTING
+    if (name == m_outputName) {
+        return;
+    }
+
+    setOutput(nullptr);
     if (name.isEmpty()) {
-        setOutput(nullptr);
         return;
     }
     auto outputs = kwinApp()->platform()->outputs();
@@ -642,6 +646,10 @@ void Device::setOutputName(const QString &name)
             break;
         }
     }
+
+    m_outputName = name;
+    writeEntry(ConfigKey::OutputName, name);
+    Q_EMIT outputNameChanged();
 #else
     Q_UNUSED(name)
 #endif
@@ -654,19 +662,7 @@ Output *Device::output() const
 
 void Device::setOutput(Output *output)
 {
-#ifndef KWIN_BUILD_TESTING
     m_output = output;
-    if (m_output) {
-        m_outputName = output->name();
-        writeEntry(ConfigKey::OutputName, output->name());
-    } else {
-        m_outputName = QString();
-        writeEntry(ConfigKey::OutputName, QString());
-    }
-    Q_EMIT outputNameChanged();
-#else
-    Q_UNUSED(output)
-#endif
 }
 
 static libinput_led toLibinputLEDS(LEDs leds)