document wxProgressDialog::Update(maximumValue) behaviour and warn the user that it may generate unwanted re-entrancies because of wxDialog::ShowModal()

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@59431 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/generic/progdlgg.cpp

@@ -411,6 +411,9 @@ wxProgressDialog::Update(int value, const wxString& newmsg, bool *skip)
             //       should be no side-effects
             wxEventLoopBase::GetActive()->YieldFor(wxEVT_CATEGORY_UI);
 
+            // NOTE: this call results in a new event loop being created
+            //       and to a call to ProcessPendingEvents() (which may generate
+            //       unwanted re-entrancies).
             (void)ShowModal();
         }
         else // auto hide