CppTools: Use fallback project part if project is closed

...instead of sticking to the old one.

If a project is closed, the editor should reflect that. It also simplifies the code.

Change-Id: I9b8a94513d3b06a238cfc4ee60c11c0d0da3d93f
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/cpptools/baseeditordocumentparser.h

@@ -47,7 +47,6 @@ public:
     static Ptr get(const QString &filePath);
 
     struct Configuration {
-        bool stickToPreviousProjectPart = true;
         bool usePrecompiledHeaders = false;
         QByteArray editorDefines;
         ProjectPart::Ptr manuallySetProjectPart;
@@ -95,10 +94,9 @@ protected:
     State state() const;
     void setState(const State &state);
 
-    static ProjectPartInfo determineProjectPart(
-            const QString &filePath,
+    static ProjectPartInfo determineProjectPart(const QString &filePath,
             const Configuration &config,
-            const State &state,
+            const ProjectPartInfo &currentProjectPartInfo,
             const ProjectExplorer::Project *activeProject,
             Language languagePreference,
             bool hasActiveProjectChanged);