Avoid using wxString::Empty()

This is confusingly similar to std::string::empty() which doesn't do the
same thing, so prefer using clear() instead.

And simply remove Empty() calls before the assignment, as they're
useless.

No real changes.

include/wx/dirdlg.h

@@ -94,7 +94,11 @@ public:
         return m_path;
     }
 
-    virtual void GetPaths(wxArrayString& paths) const { paths.Empty(); paths.Add(m_path); }
+    virtual void GetPaths(wxArrayString& paths) const
+    {
+        paths.clear();
+        paths.push_back(m_path);
+    }
 
 protected:
     wxString m_message;

src/gtk/dirdlg.cpp

@@ -196,7 +196,6 @@ wxString wxDirDialog::GetPath() const
 
 void wxDirDialog::GetPaths(wxArrayString& paths) const
 {
-    paths.Empty();
     paths = m_paths;
 }
 

src/osx/cocoa/dirdlg.mm

@@ -179,7 +179,6 @@ wxString wxDirDialog::GetPath() const
 
 void wxDirDialog::GetPaths(wxArrayString& paths) const
 {
-    paths.Empty();
     paths = m_paths;
 }