CompilationDatabaseProjectManager: Fix cached state being unhandled

In this code, database file is being hashed and if hash stays the same,
parser quickly returns ParseResult::Cached. But as database never gets
read, source tree isn't being built, thus dbContents() never gets called

I moved ParseGuard::markAsSuccess() call to the finish() method of parser,
so we tell ProjectExplorer that parsing finished successfully on Cached state

Change-Id: I7ea28017e653ac6e2d7f50047c09a6eb7ecda13f
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

src/plugins/compilationdatabaseprojectmanager/compilationdbparser.cpp

@@ -153,6 +153,9 @@ void CompilationDbParser::parserJobFinished()
 
 void CompilationDbParser::finish(ParseResult result)
 {
+    if (result != ParseResult::Failure)
+        m_guard.markAsSuccess();
+
     emit finished(result);
     deleteLater();
 }

src/plugins/compilationdatabaseprojectmanager/compilationdbparser.h

@@ -69,7 +69,6 @@ public:
     QList<ProjectExplorer::FileNode *> scannedFiles() const;
     DbContents dbContents() const
     {
-        m_guard.markAsSuccess();
         return m_dbContents;
     }