[LyX/master] Fix crash when dissolving a top level math inset

[Jean-Marc Lasgouttes]

commit c75522bbb7a0044f2370ced294a27738d47935ea
Author: Jean-Marc Lasgouttes <lasgouttes at lyx.org>
Date:   Wed Jun 29 22:52:16 2022 +0200

    Fix crash when dissolving a top level math inset
    
    This should be disabled not only for math hull, but also macro template.
    
    Fixes bug #12562.
---
 src/mathed/InsetMathNest.cpp |   18 ++++++++++++------
 1 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/src/mathed/InsetMathNest.cpp b/src/mathed/InsetMathNest.cpp
index cfa5aaf..05920cc 100644
--- a/src/mathed/InsetMathNest.cpp
+++ b/src/mathed/InsetMathNest.cpp
@@ -1275,13 +1275,16 @@ void InsetMathNest::doDispatch(Cursor & cur, FuncRequest & cmd)
 			cur.undispatched();
 		break;
 	}
-	case LFUN_INSET_DISSOLVE:
-		if (!asHullInset()) {
+	case LFUN_INSET_DISSOLVE: {
+		bool const enabled = cur.inMathed()
+			&& (&cur.inset() != this || cur[cur.depth() - 1].inset().inMathed());
+		if (enabled) {
 			cur.recordUndoInset();
+			// FIXME: this loses data
 			cur.pullArg();
 		}
 		break;
-
+	}
 	case LFUN_MATH_LIMITS: {
 		InsetMath * in = 0;
 		if (cur.pos() < cur.lastpos() && cur.nextMath().allowsLimitsChange())
@@ -1497,10 +1500,13 @@ bool InsetMathNest::getStatus(Cursor & cur, FuncRequest const & cmd,
 		break;
 	}
 
-	case LFUN_INSET_DISSOLVE:
-		flag.setEnabled(!asHullInset());
+	case LFUN_INSET_DISSOLVE: {
+		// Do not dissolve a math inset which is in text
+		bool const enabled = cur.inMathed()
+			&& (&cur.inset() != this || cur[cur.depth() - 1].inset().inMathed());
+		flag.setEnabled(enabled);
 		break;
-
+	}
 	case LFUN_PASTE: {
 		docstring const & name = cmd.argument();
 		if (name == "html" || name == "latex")