[LyX/master] Disable Edit Externally for read-only Buffers.

[Richard Kimberly Heck]

commit c978137f99dd7ea6655829a420e10b402ef4efef
Author: Richard Kimberly Heck <rikiheck at lyx.org>
Date:   Sun Dec 6 00:14:23 2020 -0500

    Disable Edit Externally for read-only Buffers.
---
 src/insets/InsetCollapsible.cpp |    6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/src/insets/InsetCollapsible.cpp b/src/insets/InsetCollapsible.cpp
index 1e5473d..58f45b5 100644
--- a/src/insets/InsetCollapsible.cpp
+++ b/src/insets/InsetCollapsible.cpp
@@ -651,11 +651,13 @@ bool InsetCollapsible::getStatus(Cursor & cur, FuncRequest const & cmd,
 		return true;
 
 	case LFUN_INSET_EDIT:
-		flag.setEnabled(getLayout().editExternally() && tempfile_ == nullptr);
+		flag.setEnabled(!buffer().hasReadonlyFlag() &&
+			getLayout().editExternally() && tempfile_ == nullptr);
 		return true;
 
 	case LFUN_INSET_END_EDIT:
-		flag.setEnabled(getLayout().editExternally() && tempfile_ != nullptr);
+		flag.setEnabled(!buffer().hasReadonlyFlag() &&
+			getLayout().editExternally() && tempfile_ != nullptr);
 		return true;
 
 	default: