Reapplied clang-tidy filters

- modernize-use-nullptr
- modernize-redundant-void-arg
- readability-simplify-boolean-expr
- misc-redundant-expression
- readability-redundant-control-flow
- readability-avoid-const-params-in-decls

rtgui/progressconnector.h

@@ -90,7 +90,7 @@ class ProgressConnector
 
 public:
 
-    ProgressConnector (): retval( 0 ), workThread( nullptr ) { }
+    ProgressConnector (): retval( nullptr ), workThread( nullptr ) { }
 
     void startFunc (const sigc::slot0<T>& startHandler, const sigc::slot0<bool>& endHandler )
     {