Fix for bug 1550 - metadata editor: esc does not cancel

Problem: on Windows, Esc does not cancel metadata editor.

Fix:
1. In tag.h, for windows, don't override IsEscapeKey().
2. In tag.cpp, for windows, include a return in the function DoCancel, so that if a cell is being edited and the user presses Esc, this just cancels the edit, and not the dialog.

This fix returns the behaviour of the dialog on Windows back to the behaviour prior to commit c1ca055. It only affects the behaviour on Windows.

src/Tags.cpp

@@ -1365,6 +1365,9 @@ void TagsEditor::DoCancel(bool escKey)
       // To avoid memory leak, don't forget DecRef()!
       editor->DecRef();
       mGrid->HideCellEditControl();
+#if defined(__WXMSW__)
+      return;
+#endif
    }
 
    auto focus = wxWindow::FindFocus();

src/Tags.h

@@ -142,7 +142,9 @@ class TagsEditor final : public wxDialogWrapper
 
    virtual ~TagsEditor();
 
+#if !defined(__WXMSW__)
    bool IsEscapeKey(const wxKeyEvent& /*event*/) override { return false; }
+#endif
 
    void PopulateOrExchange(ShuttleGui & S);