win32: Fix crash from win32 surface's image size too small

Beginning in 1.12, a crash can occur when the win32 surface's image size
does not cover the entire surface (e.g. due to clipping regions).

This patch enlarges the fallback surface created of the amount
necessary not to write past the end of the DIB. It assumes that
Clip applied to an HDC are clamped to (0,0,width,height) of the HDC.

Fixes: https://bugs.freedesktop.org/show_bug.cgi?id=53121
Reviewed-by: Bryce Harrington <bryce@osg.samsung.com>

src/win32/cairo-win32-display-surface.c

@@ -455,17 +455,17 @@ _cairo_win32_display_surface_map_to_image (void                    *abstract_sur
 	surface->fallback =
 	    _cairo_win32_display_surface_create_for_dc (surface->win32.dc,
 							surface->win32.format,
-							surface->win32.extents.width,
-							surface->win32.extents.height);
+							surface->win32.extents.x + surface->win32.extents.width,
+							surface->win32.extents.y + surface->win32.extents.height);
 	if (unlikely (status = surface->fallback->status))
 	    goto err;
 
 	if (!BitBlt (to_win32_surface(surface->fallback)->dc,
-		     0, 0,
+		     surface->win32.extents.x, surface->win32.extents.y,
 		     surface->win32.extents.width,
 		     surface->win32.extents.height,
 		     surface->win32.dc,
-		     0, 0,
+		     surface->win32.extents.x, surface->win32.extents.y,
 		     SRCCOPY)) {
 	    status = _cairo_error (CAIRO_STATUS_DEVICE_ERROR);
 	    goto err;