XRegion has to match the "real" XRegion structure

i.e. same as...

commit 5470a365f25e5052b4dd74f76aa2196f0d70934b
Author: Caolán McNamara <caolanm@redhat.com>
Date:   Wed Nov 25 10:04:37 2015 +0000

    XRegion has to match the "real" XRegion structure, even if we don't use

    some of the fields

    regression from

    commit dd351dd728687cffe432ce0ec9367ceb80e097fb
    Date:   Tue Nov 24 08:50:39 2015 +0200

        loplugin:unusedfields in vcl/

Change-Id: I8314eae6d507b6a7fb847d593458e15e666230c8
diff --git a/vcl/unx/generic/gdi/x11cairotextrender.cxx b/vcl/unx/generic/gdi/x11cairotextrender.cxx
index 290f638..4f6cc9f 100644
--- a/vcl/unx/generic/gdi/x11cairotextrender.cxx
+++ b/vcl/unx/generic/gdi/x11cairotextrender.cxx
@@ -29,10 +29,22 @@ struct BOX
{
    short x1, x2, y1, y2;
};

/*
 * Xutil.h contains the declaration:
 * typedef struct _XRegion *Region;
 *
 * this struct has to match the real _Xregion
 * definition, don't change this is remove apparently
 * unused fields
 */

struct _XRegion
{
    long size;
    long numRects;
    BOX *rects;
    BOX extents;
};

X11CairoTextRender::X11CairoTextRender(X11SalGraphics& rParent)