more uniform treatment of properties (but < 0 should not occur here);

--- a/src/Pure/General/position.ML	Sat Apr 01 14:59:42 2023 +0200
+++ b/src/Pure/General/position.ML	Sat Apr 01 15:01:35 2023 +0200
@@ -208,7 +208,7 @@
     end_offset = Properties.get_int props Markup.end_offsetN,
     props = props};
 
-fun int_entry k i = if invalid i then [] else [(k, Value.print_int i)];
+fun int_entry k i = if i = 0 then [] else [(k, Value.print_int i)];
 
 fun properties_of (Pos {line, offset, end_offset, props}) =
   int_entry Markup.lineN line @