Fix splitting message into title in body in MSW wxProgressDialog.

If the message doesn't contain any new lines, it should be used as the body,
not the title as having title without body doesn't make sense and looks
strange.

Closes #13441.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@69592 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/msw/progdlg.cpp

@@ -236,6 +236,11 @@ void PerformNotificationUpdates(HWND hwnd,
             body.assign(title, posNL + numNLs, wxString::npos);
             title.erase(posNL);
         }
+        else // A single line
+        {
+            // Don't use title without the body, this doesn't make sense.
+            title.swap(body);
+        }
 
         ::SendMessage( hwnd,
                        TDM_SET_ELEMENT_TEXT,