Fix resource leak

CID 178811 (#1 of 1): Resource leak (RESOURCE_LEAK)
25. leaked_storage: Variable dptr going out of scope leaks the storage it points to.

Change-Id: I3354fe46cfb08701f387f65aaaa5c4f235079501
Coverity-Id: 178811
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>

src/plugins/platforms/xcb/nativepainting/qpixmap_x11.cpp

@@ -1549,6 +1549,7 @@ QPixmap QX11PlatformPixmap::transformed(const QTransform &transform, Qt::Transfo
     if (!qt_xForm_helper(mat, xi->xoffset, type, bpp, dptr, xbpl, p_inc, h, sptr, sbpl, ws, hs)){
         qWarning("QPixmap::transform: display not supported (bpp=%d)",bpp);
         QPixmap pm;
+        free(dptr);
         return pm;
     }