Add missing define guards

Ammend 98c921c0e2250ce85ab3de05ea58e98587102ae3 to use m_composeState
only if xcbcommon is available.

Pick-to: 5.15
Change-Id: I48332b15def3282c5bda3e1c7c393ea7e9849cbe
Reviewed-by: Aleix Pol Gonzalez <aleixpol@kde.org>

src/plugins/platforms/wayland/qwaylandinputcontext.cpp

@@ -408,8 +408,10 @@ bool QWaylandInputContext::isValid() const
 void QWaylandInputContext::reset()
 {
     qCDebug(qLcQpaInputMethods) << Q_FUNC_INFO;
+#if QT_CONFIG(xkbcommon)
     if (m_composeState)
         xkb_compose_state_reset(m_composeState);
+#endif
 
     QPlatformInputContext::reset();