Support GUIs with a single PI and no RI

templates/skeletons/gui-enum-defs/function.tmplt

@@ -32,7 +32,11 @@
 */
 #pragma once
 
-@@IF@@ @_List_Of_ASync_PIs'Length_@ > 1  @@-- include "Poll"
+@@-- the list of PIs may include "Poll" if there are RIs
+@@-- so we must create the type either if there is more than one element in
+@@-- the list, or of there is only one but it is not "poll"
+// @_List_Of_ASync_PIs'Length_@ @_LOWER:List_Of_ASync_PIs_@
+@@IF@@ @_List_Of_ASync_PIs'Length_@ > 1 or (@_List_Of_ASync_PIs'Length_@ = 1 and @_LOWER:List_Of_ASync_PIs_@ /= poll)
 typedef enum {
 @@INLINE(   )(,\n   )()@@
     @@TABLE@@