QbsProjectManager: Update the code model even if the project is empty.

This is the right thing to do. For instance, without this patch, after
removing all files from a project the code model still believes they are
there.

Change-Id: I848dbeca865b495aa26483460a0547c8215055f9
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@theqtcompany.com>

src/plugins/qbsprojectmanager/qbsproject.cpp

@@ -797,8 +797,6 @@ void QbsProject::updateCppCodeModel()
         }
     }
 
-    if (pinfo.projectParts().isEmpty())
-        return;
     pinfo.finish();
 
     QtSupport::UiCodeModelManager::update(this, uiFiles);