Sequencer - Make sure that selection is valid

When something is selected, it can become invalid due to e.g. undo or
file reload, so we need to NOT CRASH like a turd.

ui-sequencer.cc

@@ -217,8 +217,11 @@ struct T_SyncViewImpl_
 		POINT_VALUE ,
 	};
 
-	// Make sure all displayed curves/inputs/overrides still exist
+	// Make sure all displayed inputs/overrides still exist
-	void checkSelectedCurves( ) noexcept;
+	void checkTracks( ) noexcept;
+	// Make sure the currently selected track/segment/point is still valid
+	void checkSelection( ) noexcept;
+	// Display the toolbar
 	void displayToolbar( ) noexcept;
 
 	//----------------------------------------------------------------------
@@ -340,17 +343,38 @@ bool T_SyncViewImpl_::display( ) noexcept
 		return false;
 	}
 
-	checkSelectedCurves( );
+	checkTracks( );
+	checkSelection( );
 	displayToolbar( );
 
-	//----------------------------------------------------------------------
+	// Sequencer widget
-	// Sequencer widget & subwindows
-
 	PushItemWidth( -1 );
 	sequencerWidget( );
 	PopItemWidth( );
 	End( );
 
+	// Close sub-window if e.g. selection has changed
+	switch( sub ) {
+	    case SW_POINT:
+		if ( !selPoint ) {
+			sub = SW_SEGMENT;
+		}
+		// fallthrough
+	    case SW_SEGMENT:
+		if ( !selSegment ) {
+			sub = SW_TRACK;
+		}
+		// fallthrough
+	    case SW_TRACK:
+		if ( !selId ) {
+			sub = SW_NONE;
+		}
+		break;
+
+	    default: break;
+	}
+
+	// Display selected sub-window
 	switch ( sub ) {
 	    case SW_NONE:
 		break;
@@ -376,7 +400,7 @@ bool T_SyncViewImpl_::display( ) noexcept
 	return true;
 }
 
-void T_SyncViewImpl_::checkSelectedCurves( ) noexcept
+void T_SyncViewImpl_::checkTracks( ) noexcept
 {
 	auto& sync{ Common::Sync( ) };
 
@@ -418,6 +442,50 @@ void T_SyncViewImpl_::checkSelectedCurves( ) noexcept
 	}
 }
 
+void T_SyncViewImpl_::checkSelection( ) noexcept
+{
+	if ( !selId ) {
+		return;
+	}
+	assert( !selIsOverride ); // XXX
+	auto const* const curve{ Common::Sync( ).getCurve( selId ) };
+
+	// Missing curve
+	if ( !curve ) {
+		// Remove segment/point selection
+		if ( selSegment ) {
+			selSegment.clear( );
+			selPoint.clear( );
+		}
+		// If there's no matching input, unselect the track
+		if ( !Common::Sync( ).hasInput( selId ) ) {
+			selId = T_String{};
+		}
+	} else {
+		// No segment selected? We're ok.
+		if ( !selSegment ) {
+			return;
+		}
+
+		// Check segment and point
+		if ( *selSegment >= curve->segments.size( ) ) {
+			selSegment.clear( );
+			selPoint.clear( );
+		} else if ( selPoint && *selPoint >= curve->segments[
+				*selSegment ].values.size( ) ) {
+			selPoint.clear( );
+		} else {
+			return;
+		}
+	}
+	// If we were doing something with the curve, get rid of that too
+	if ( selUpdate != E_ChangeType::NONE ) {
+		selUpdate = E_ChangeType::NONE;
+		selUpdatingCopy.clear( );
+		selUpdatingOriginal.clear( );
+	}
+}
+
 void T_SyncViewImpl_::displayToolbar( ) noexcept
 {
 	using namespace ImGui;