[LyX/master] Fix part of bug #8521.

[Richard Kimberly Heck]

commit b1f1b2321b01ac2b17bb37147fea1a5aea26e487
Author: Richard Kimberly Heck <rikih...@lyx.org>
Date:   Thu Oct 4 21:02:51 2018 -0400

    Fix part of bug #8521.
---
 src/mathed/InsetMathDelim.cpp |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/src/mathed/InsetMathDelim.cpp b/src/mathed/InsetMathDelim.cpp
index 809e8a0..6a2be5e 100644
--- a/src/mathed/InsetMathDelim.cpp
+++ b/src/mathed/InsetMathDelim.cpp
@@ -182,11 +182,15 @@ void InsetMathDelim::mathematica(MathematicaStream & os) 
const
 void InsetMathDelim::mathmlize(MathStream & os) const
 {
        os << "<mo form='prefix' fence='true' stretchy='true' symmetric='true'>"
+          << "<mrow>"
           << convertDelimToXMLEscape(left_)
+          << "</mrow>"
           << "</mo>\n"
           << cell(0)
           << "\n<mo form='postfix' fence='true' stretchy='true' 
symmetric='true'>"
+          << "<mrow>"
           << convertDelimToXMLEscape(right_)
+          << "</mrow>"
           << "</mo>\n";
 }