DIALOG_LABEL_PROPERTIES: allows entering spaces in label names.

This issue was created by switching to FILTER_COMBOBOX in this dialog.
Spaces in labels are not a good idea, but this is needed to enter group
members to a bus definition

Fixes https://gitlab.com/kicad/code/kicad/-/issues/21300

(cherry picked from commit a0485a38a7)

eeschema/dialogs/dialog_label_properties.cpp

@@ -421,6 +421,14 @@ void DIALOG_LABEL_PROPERTIES::OnCBValueCharHook( wxKeyEvent& aEvent )
     // and we only want to accept the entered string.
     if( aEvent.GetKeyCode() == WXK_RETURN )
         wxPostEvent( this, wxCommandEvent( wxEVT_COMMAND_BUTTON_CLICKED, wxID_OK ) );
+    else if( aEvent.GetKeyCode() == WXK_SPACE )
+    {
+        // our FILTER_COMBOBOX uses the space as special command, not wanted here,
+        // to open the dropdown list of labels.
+        // So just add the space char to the current text, at current insertion point,
+        // and do not skip this event
+        m_activeTextEntry->WriteText( wxT(" " ) );
+    }
     else
         aEvent.Skip();
 }