CppunitTest_sw_ooxmlsdrexport: make this failure a bit more readable

Change-Id: Ia71f5ea712ad16d6eef3af1136613d38cd27b581

sw/qa/extras/ooxmlexport/ooxmlsdrexport.cxx

@@ -201,7 +201,8 @@ DECLARE_OOXMLEXPORT_TEST(testDmlRectangleRelsize, "dml-rectangle-relsize.docx")
 {
     // This was around 19560, as we did not read wp14:pctHeight for
     // drawinglayer shapes and the fallback data was invalid.
-    CPPUNIT_ASSERT(getShape(1)->getSize().Height >= 20992);
+    OString aMessage("Height is only " + OString::number(getShape(1)->getSize().Height));
+    CPPUNIT_ASSERT_MESSAGE(aMessage.getStr(), getShape(1)->getSize().Height >= 20992);
 
     // This was around 0: relative size of 0% was imported as 0, not "fall back to absolute size".
     CPPUNIT_ASSERT(getShape(2)->getSize().Height > 300);