CMake: Delete watched files when closing a project

Fixes a crash when re-opening a cmake project.

Change-Id: I5fc747f19787594964fe55c19e29e944c4a5092d
Reviewed-by: Benjamin Zeller <benjamin.zeller@canonical.com>
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/cmakeprojectmanager/cmakeproject.cpp

@@ -105,6 +105,7 @@ CMakeProject::~CMakeProject()
 {
     setRootProjectNode(nullptr);
     m_codeModelFuture.cancel();
+    qDeleteAll(m_watchedFiles);
     qDeleteAll(m_extraCompilers);
 }