Legacy mode: Pan with mouse middle button fix an unwanted displacement of the drawings (half width of scroll bars) when starting the pan (due to a parameter (new reference position of scroll bars in IU) which was stored with an incorrect value)

Minor enhancement during pan: the mouse cursor shape is modified.

common/draw_frame.cpp

@@ -1035,10 +1035,11 @@ void EDA_DRAW_FRAME::AdjustScrollBars( const wxPoint& aCenterPositionIU )
     double unitsX = virtualSizeIU.x * scale;
     double unitsY = virtualSizeIU.y * scale;
 
+    // Store the requested center position for later use
+    SetScrollCenterPosition( aCenterPositionIU );
+
     // Calculate the scroll bar position in internal units to place the
     // center position at the center of client rectangle.
-    SetScrollCenterPosition( centerPositionIU );
-
     double posX = centerPositionIU.x - clientRectIU.GetWidth()  / 2.0 - screen->m_DrawOrg.x;
     double posY = centerPositionIU.y - clientRectIU.GetHeight() / 2.0 - screen->m_DrawOrg.y;