If string are empty, DoGetTextExtent should not return descent by a random value

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@77786 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/x11/dcclient.cpp

@@ -1660,6 +1660,13 @@ void wxWindowDCImpl::DoGetTextExtent( const wxString &string, wxCoord *width, wx
     {
         if (width) (*width) = 0;
         if (height) (*height) = 0;
+
+        //empty string should also make sure the descent and leading is zero.
+        if (descent)
+        {
+            (*descent) = 0;
+        }
+        if (externalLeading) (*externalLeading) = 0;
         return;
     }