Allow setting hints for multi-line wxTextCtrl when supported.

Don't prevent people from using hints in wxMSW and wxGTK2, where they work
with multiline text controls too, even though they do not work with wxGTK3 nor
wxOSX.

Closes #14456.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@78316 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/gtk/textentry.cpp

@@ -521,7 +521,7 @@ bool wxTextEntry::SetHint(const wxString& hint)
 {
 #if GTK_CHECK_VERSION(3,2,0)
     GtkEntry *entry = GetEntry();
-    if (entry && gtk_check_version(3,2,0) == NULL)
+    if (entry && GTK_IS_ENTRY(entry) && gtk_check_version(3,2,0) == NULL)
     {
         gtk_entry_set_placeholder_text(entry, wxGTK_CONV(hint));
         return true;