Check for existence of QML import paths.

Filter out module QML import paths that point to 
nonexistent file system paths.

Change-Id: I897ef50593eeb46c6c9eaec27313ec12e6113cb6
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@digia.com>

mkspecs/features/qt.prf

@@ -83,7 +83,7 @@ contains(qt_module_deps, qml): \
     qtPrepareTool(QMLIMPORTSCANNER, qmlimportscanner)
     for (MODULE, QT_MODULES) {
         PATH = $$eval(QT.$${MODULE}.qml)
-        !isEmpty(PATH): QMLPATHS += $$PATH
+        !isEmpty(PATH):exists($$PATH): QMLPATHS += $$PATH
     }
     QMLPATHS = $$unique(QMLPATHS)
     for (QMLPATH, QMLPATHS): \