fix the error message for lone quantifiers

Author: pygy

src/core.js

@@ -330,7 +330,7 @@ const hasLoneQuantifierBracket = mdMemo('hasLoneQuantifierBracket', function has
 		} else {
 			if (result[1] === '[') inCClass = true
 			else if (result[1] === ']') continue
-			else return true
+			else return result[1]
 		}
 	}
 	return false

tests/tests.js

@@ -544,7 +544,9 @@ o.spec("flags", function () {
 		})
 		o("lone brackets are rejected even in non-unicode context", function() {
 			o(()=>sequence(/{/, 'x')).throws(SyntaxError)
+			o(()=>sequence(/{/, 'x')).throws("Lone quantifier bracket { in /{/")
 			o(()=>sequence('x', /}/)).throws(SyntaxError)
+			o(()=>sequence('x', /}/)).throws("Lone quantifier bracket } in /}/")
 		})
 
 		o("No unnecessary escapes", function () {