Fixed a minor bug in how the zoomable_region widget

drew itself after a resize in some cases.

--HG--
extra : convert_revision : svn%3Afdd8eb12-d10e-0410-9acb-85c331704f74/trunk%402667

dlib/gui_widgets/base_widgets.cpp

@@ -2071,15 +2071,16 @@ namespace dlib
         parent.invalidate_rectangle(rect+old);
 
         const double old_scale = scale;
+        const vector<double> old_gr_orig(gr_orig);
         scale = min_scale;
+        gr_orig = vector<double>(0,0,0);
         lr_point = gui_to_graph_space(point(display_rect_.right(),display_rect_.bottom()));
         scale = old_scale;
 
         // call adjust_origin() so that the scroll bars get their max slider positions
         // setup right
         const point rect_corner(display_rect_.left(), display_rect_.top());
-        const vector<double> rect_corner_graph(gui_to_graph_space(rect_corner));
-        adjust_origin(rect_corner, rect_corner_graph);
+        adjust_origin(rect_corner, old_gr_orig);
     }
 
 // ----------------------------------------------------------------------------------------

dlib/gui_widgets/base_widgets.h

@@ -2251,7 +2251,7 @@ namespace dlib
         rectangle display_rect_;
 
         bool mouse_drag_screen;  // true if the user is dragging the white background area
-        point drag_screen_point; // the starting point the mouse was at in graph space for the background area drag
+        vector<double> drag_screen_point; // the starting point the mouse was at in graph space for the background area drag
 
         scroll_bar vsb;
         scroll_bar hsb;