Fixed several issues detected during testing / review (refs #304)

* MS report 1-5 https://dev.vatsim-germany.org/issues/304#change-1800
* Clang warning https://dev.vatsim-germany.org/boards/22/topics/1982?r=1997#message-1997
* Wrong indexes for dockable widgets, RW: https://dev.vatsim-germany.org/issues/304#note-13
* Fixed wrong offset in Fsuipc class
* Improved position handling for floating widgets opened 1st time

src/blackgui/dockwidget.h

@@ -66,9 +66,12 @@ namespace BlackGui
         //! Was widget already floating
         bool wasAlreadyFloating() const { return this->m_wasAlreadyFloating; }
 
-        //! Size when floating
+        //! Size when floating first time
         void setPreferredSizeWhenFloating(const QSize &size) { this->m_preferredSizeWhenFloating = size; }
 
+        //! Position offset when floating first time
+        void setOffsetWhenFloating(const QPoint &point) { this->m_offsetWhenFloating = point; }
+
     public slots:
         //! Toggle floating
         void toggleFloating();
@@ -109,7 +112,8 @@ namespace BlackGui
         QString m_windowTitleBackup;    //!< original title, even if the widget title is deleted for layout purposes
         bool m_windowTitleWhenDocked = true;
         bool m_wasAlreadyFloating = false;
-        QSize m_preferredSizeWhenFloating;
+        QSize m_preferredSizeWhenFloating; //!< preferred size men floating 1st time
+        QPoint m_offsetWhenFloating;  //!< initial offset to main window when floating first time
 
         //! Empty widget with no size
         void initTitleBarWidgets();