[LyX/master] fix compiler warning

[Juergen Spitzmueller]

commit f6fff878a787f87a36dd8aef3e2aee9d4c0765bc
Author: Juergen Spitzmueller <spitz at lyx.org>
Date:   Tue Aug 16 17:41:40 2022 +0200

    fix compiler warning
---
 src/mathed/InsetMathXArrow.cpp |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/src/mathed/InsetMathXArrow.cpp b/src/mathed/InsetMathXArrow.cpp
index c150a44..cd36fe1 100644
--- a/src/mathed/InsetMathXArrow.cpp
+++ b/src/mathed/InsetMathXArrow.cpp
@@ -133,6 +133,7 @@ docstring map_latex_to(docstring latex, bool xml = false)
 		std::string format = (xml) ? "XML" : "HTML";
 		lyxerr << "mathmlize " << format << " conversion for '" << latex << "' not implemented" << endl;
 		LASSERT(false, return from_ascii(dict["xrightarrow"]));
+		return docstring();
 	}
 }