When cleaning up before quitting, take care of exceptions

We do not want the cleanup work to be interrupted by a buffer exception.

Spotted by coverity. See bug #9979 for discussion.

(cherry picked from commit 0d565f7b35)

src/LyX.cpp

@@ -380,8 +380,12 @@ void LyX::prepareExit()
 	// Write the index file of the converter cache
 	ConverterCache::get().writeIndex();
 
+	// closing buffer may throw exceptions, but we ignore them since we
+	// are quitting.
+	try {
 		// close buffers first
 		pimpl_->buffer_list_.closeAll();
+	} catch (ExceptionMessage const &) {}
 
 	// register session changes and shutdown server and socket
 	if (use_gui) {