Fix Fl_OpenGL_Display_Device::capture_gl_rectangle(Fl_Gl_Window*) by …

…making current the window's GL context.

The problem was visible with test/cube: when the window was minimized, only the left GL subwindow
was captured in the window icon.

git-svn-id: file:///fltk/svn/fltk/branches/branch-1.4@13066 ea41ed52-d2ee-0310-a9c1-e6b18d33e121

src/drivers/OpenGL/Fl_OpenGL_Display_Device.cxx

@@ -69,6 +69,7 @@ Fl_RGB_Image* Fl_OpenGL_Display_Device::capture_gl_rectangle(Fl_Gl_Window* glw,
     w *= factor; h *= factor; x *= factor; y *= factor;
   }
   Fl_Cocoa_Gl_Window_Driver *driver = (Fl_Cocoa_Gl_Window_Driver*)glw->gl_driver();
+  driver->GLcontext_makecurrent(glw->context());
   driver->flush_context(); // to capture also the overlay and for directGL demo
   // Read OpenGL context pixels directly.
   // For extra safety, save & restore OpenGL states that are changed