Don't test if a reference is null, this cannot happen.

Testing for null references is unnecessary and just results in clang warnings.

Closes #17016.

src/propgrid/props.cpp

@@ -1201,7 +1201,7 @@ wxEnumProperty::wxEnumProperty( const wxString& label, const wxString& name,
 {
     SetIndex(0);
 
-    if ( &labels && !labels.empty() )
+    if ( !labels.empty() )
     {
         m_choices.Set(labels, values);
 
@@ -1590,7 +1590,7 @@ wxFlagsProperty::wxFlagsProperty( const wxString& label, const wxString& name,
 {
     m_oldChoicesData = NULL;
 
-    if ( &labels && !labels.empty() )
+    if ( !labels.empty() )
     {
         m_choices.Set(labels,values);