Don't build ibus when dbus is not available

Change-Id: I0011cae034f186f239f486f5d83635bf4d11b88d
Reviewed-on: http://codereview.qt-project.org/4879
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Lars Knoll <lars.knoll@nokia.com>

src/plugins/platforminputcontexts/platforminputcontexts.pro

@@ -1,4 +1,4 @@
 TEMPLATE = subdirs
-
+contains(QT_CONFIG, dbus) {
 !macx:!win32:SUBDIRS += ibus
-
+}