fix: add implied exception comp to item for single item variant

When adding an implied "in" comparison to an exception using the
single value form, add it to item, not items.

This fixes #1984.

Signed-off-by: Mark Stemm <mark.stemm@gmail.com>

userspace/engine/rule_loader.cpp

@@ -152,7 +152,7 @@ static void validate_exception_info(
 		if (!ex.comps.is_valid())
 		{
 			ex.comps.is_list = false;
-			ex.comps.items.push_back({false, "in"});
+			ex.comps.item = "in";
 		}
 		THROW(ex.comps.is_list, "Rule exception item "
 			+ ex.name + ": fields and comps must both be strings");