Ban continue in a double-curly while loop

lang/parse/parse.go

diff --git a/lang/parse/parse.go b/lang/parse/parse.go
index 994dd22..4bf02fb 100644
--- a/lang/parse/parse.go
+++ b/lang/parse/parse.go
@@ -816,7 +816,12 @@
 			return nil, fmt.Errorf(`parse: expected endwhile%s at %s:%d`,
 				dotLabel, p.filename, p.line())
 		}
-		if doubleCurly && !a.Terminates(body) {
+		if !doubleCurly {
+			// No-op.
+		} else if n.HasContinue() {
+			return nil, fmt.Errorf(`parse: double {{ }} while loop has explicit continue at %s:%d`,
+				p.filename, p.line())
+		} else if !a.Terminates(body) {
 			return nil, fmt.Errorf(`parse: double {{ }} while loop doesn't terminate at %s:%d`,
 				p.filename, p.line())
 		}