Don't clear selection during session load

Mouse-mode is set after the the session sets CoreSelection
in the backend, and can clear valid selection.

Note: Region Selection (if any) is saved in instant.xml
and set during first_idle, which usually still happens
from `load_session_stage_two() -> flush_pending()`.

gtk2_ardour/ardour_ui.cc

@@ -349,6 +349,7 @@ ARDOUR_UI::ARDOUR_UI (int *argcp, char **argvp[], const char* localedir)
 	, recorder_visibility_button (S_("Window|Rec"))
 	, trigger_page_visibility_button (S_("Window|Cue"))
 	, nsm_first_session_opened (false)
+	, _loading_session (false)
 {
 	Gtkmm2ext::init (localedir);
 

gtk2_ardour/ardour_ui.h

@@ -257,6 +257,8 @@ public:
 	bool ask_about_loading_existing_session (const std::string& session_path);
 	int load_session_from_startup_fsm ();
 
+	bool loading_session () const { return _loading_session; }
+
 	/// @return true if session was successfully unloaded.
 	int unload_session (bool hide_stuff = false, bool force_unload = false);
 	void close_session();
@@ -874,6 +876,8 @@ private:
 	void ask_about_scratch_deletion ();
 	bool nsm_first_session_opened;
 
+	bool _loading_session;
+
 	PBD::ScopedConnectionList clock_state_connection;
 };
 

gtk2_ardour/ardour_ui_session.cc

@@ -404,6 +404,8 @@ ARDOUR_UI::audio_midi_setup_reconfigure_done (int response, std::string path, st
 int
 ARDOUR_UI::load_session_stage_two (const std::string& path, const std::string& snap_name, std::string mix_template)
 {
+	PBD::Unwinder uw (_loading_session, true);
+
 	Session *new_session;
 	int retval = -1;
 

gtk2_ardour/editor_mouse.cc

@@ -244,6 +244,10 @@ Editor::internal_editing() const
 void
 Editor::update_time_selection_display ()
 {
+	if (ARDOUR_UI::instance()->loading_session ()) {
+		/* leave selection alone */
+		return;
+	}
 	auto mouse_mode = current_mouse_mode ();
 	switch (mouse_mode) {
 	case MouseRange: