[LyX/master] Use proper minus sign character in MathML Core.

[Thibaut Cuvelier]

commit 790c15373782510d912ab3bd2c24393cda7fe85d
Author: Thibaut Cuvelier <tcuvelier at lyx.org>
Date:   Sat Sep 28 16:47:58 2024 +0200

    Use proper minus sign character in MathML Core.
    
    Fixes bug https://www.lyx.org/trac/ticket/13067.
    
    Based on the patch in the ticket above by Jean-Marc Lasgouttes.
---
 src/mathed/InsetMathChar.cpp | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/src/mathed/InsetMathChar.cpp b/src/mathed/InsetMathChar.cpp
index ebc1644af5..7e57bf28e5 100644
--- a/src/mathed/InsetMathChar.cpp
+++ b/src/mathed/InsetMathChar.cpp
@@ -239,6 +239,12 @@ void InsetMathChar::mathmlize(MathMLStream & ms) const
 	case '<': entity = "<"; break;
 	case '>': entity = ">"; break;
 	case '&': entity = "&"; break;
+	case '-':
+		if (ms.version() == MathMLStream::mathmlCore) {
+			// − U+2212 MINUS SIGN
+			entity = "&#x2212;";
+		}
+		break;
 	case ' ': {
 		ms << from_ascii(" ");
 		return;