QmlDesigner: Do not open another QML file in fake project mode

If a fake project is is opened the user has already opened
the "correct" .ui.qml file. We do not have to open another one.

Change-Id: Ib7e838118a9162cdc7b7aba05c51a9271503a103
Reviewed-by: Burak Hancerli <burak.hancerli@qt.io>
Reviewed-by: Thomas Hartmann <thomas.hartmann@qt.io>

src/plugins/qmlprojectmanager/buildsystem/qmlbuildsystem.cpp

@@ -380,6 +380,9 @@ Utils::FilePath QmlBuildSystem::getStartupQmlFileWithFallback() const
     if (!target())
         return {};
 
+    if (projectFilePath().endsWith(Constants::fakeProjectName))
+        return {};
+
     const auto getFirstFittingFile = [](const Utils::FilePaths &files) -> Utils::FilePath {
         for (const auto &file : files) {
             if (file.exists())