[LyX/master] Only set buffer if it is not null.

[Richard Kimberly Heck]

commit 2ae77d50919575ad90eaa3618e2f203b3575836c
Author: Richard Kimberly Heck <rikiheck at lyx.org>
Date:   Tue Nov 24 16:57:12 2020 -0500

    Only set buffer if it is not null.
    
    Yuriy found these specific problems. They do not cause a crash, but
    they are not good.
---
 src/mathed/InsetMathMacro.cpp |    6 +++++-
 src/mathed/InsetMathNest.cpp  |    6 +++++-
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/src/mathed/InsetMathMacro.cpp b/src/mathed/InsetMathMacro.cpp
index 2ecef18..f1a84cd 100644
--- a/src/mathed/InsetMathMacro.cpp
+++ b/src/mathed/InsetMathMacro.cpp
@@ -307,7 +307,11 @@ InsetMathMacro::InsetMathMacro(Buffer * buf, docstring const & name)
 InsetMathMacro::InsetMathMacro(InsetMathMacro const & that)
 	: InsetMathNest(that), d(new Private(*that.d))
 {
-	setBuffer(*that.buffer_);
+	// FIXME This should not really be necessary, but when we are
+	// initializing the table of global macros, we create macros
+	// with no associated Buffer.
+	if (that.buffer_)
+		setBuffer(*that.buffer_);
 	d->updateChildren(this);
 }
 
diff --git a/src/mathed/InsetMathNest.cpp b/src/mathed/InsetMathNest.cpp
index ada0400..97db3cc 100644
--- a/src/mathed/InsetMathNest.cpp
+++ b/src/mathed/InsetMathNest.cpp
@@ -85,7 +85,11 @@ using cap::selClearOrDel;
 InsetMathNest::InsetMathNest(Buffer * buf, idx_type nargs)
 	: InsetMath(buf), cells_(nargs), lock_(false)
 {
-	setBuffer(*buf);
+	// FIXME This should not really be necessary, but when we are
+	// initializing the table of global macros, we create macros
+	// with no associated Buffer.
+	if (buf)
+		setBuffer(*buf);
 }