[LyX/master] Fix listpreamble breakage by 6f643e52d434

[Juergen Spitzmueller]

commit b2ca2d1e3a9bd1224b264aede88784ce571aa8e2
Author: Juergen Spitzmueller <spitz at lyx.org>
Date:   Wed Dec 2 15:25:14 2020 +0100

    Fix listpreamble breakage by 6f643e52d434
---
 src/Layout.cpp |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/src/Layout.cpp b/src/Layout.cpp
index ff123dc..63a5dc4 100644
--- a/src/Layout.cpp
+++ b/src/Layout.cpp
@@ -1193,6 +1193,10 @@ void Layout::readArgument(Lexer & lex, bool validating)
 			latexargs_));
 	latexarg & arg = lam[id];
 
+	if (listpreamble)
+		// list preamble has no delimiters by default
+		arg.nodelims = true;
+
 	bool error = false;
 	bool finished = false;
 	while (!finished && lex.isOK() && !error) {