input methods: improve closing process

Make sure it's destroyed when kwin shuts down, make sure we don't start
it, for example because it crashed when we killed it like maliit does.


(cherry picked from commit 46adeb79)

main_wayland.cpp

@@ -119,7 +119,6 @@ ApplicationWayland::ApplicationWayland(int &argc, char **argv)
     connect(&m_inputMethodCrashTimer, &QTimer::timeout, this, [this] {
         m_inputMethodCrashes = 0;
     });
-    connect(waylandServer(), &WaylandServer::terminatingInternalClientConnection, this, &ApplicationWayland::stopInputMethod);
 }
 
 ApplicationWayland::~ApplicationWayland()
@@ -230,8 +229,13 @@ void ApplicationWayland::stopInputMethod()
     if (!m_inputMethodProcess) {
         return;
     }
-    m_inputMethodProcess->kill();
-    m_inputMethodProcess->waitForFinished();
+    disconnect(m_inputMethodProcess, nullptr, this, nullptr);
+
+    m_inputMethodProcess->terminate();
+    if (!m_inputMethodProcess->waitForFinished()) {
+        m_inputMethodProcess->kill();
+        m_inputMethodProcess->waitForFinished();
+    }
     if (waylandServer()) {
         waylandServer()->destroyInputMethodConnection();
     }
@@ -242,10 +246,12 @@ void ApplicationWayland::stopInputMethod()
 void ApplicationWayland::startInputMethod(const QString &executable)
 {
     stopInputMethod();
-    if (executable.isEmpty()) {
+    if (executable.isEmpty() || isTerminating()) {
         return;
     }
 
+    connect(waylandServer(), &WaylandServer::terminatingInternalClientConnection, this, &ApplicationWayland::stopInputMethod, Qt::UniqueConnection);
+
     QStringList arguments = KShell::splitArgs(executable);
     if (arguments.isEmpty()) {
         qWarning("Failed to launch the input method server: %s is an invalid command", qPrintable(m_inputMethodServerToStart));