Fix another getSelectedSurface() relatedbug that caused crash

src/UserInterface/ProjectionEditor.cpp

@@ -191,11 +191,14 @@ namespace ofx {
         }
         
         void ProjectionEditor::updateJoints() {
-            vector<ofVec3f>& vertices =
-                surfaceManager->getSelectedSurface()->getVertices();
-            for (int i = 0; i < vertices.size(); i++) {
-                joints[i]->position = ofVec2f(vertices[i].x, vertices[i].y);
+            if (surfaceManager->getSelectedSurface()) {
+                vector<ofVec3f>& vertices =
+                    surfaceManager->getSelectedSurface()->getVertices();
+                for (int i = 0; i < vertices.size(); i++) {
+                    joints[i]->position = ofVec2f(vertices[i].x, vertices[i].y);
+                }
             }
+            
         }
         
         void ProjectionEditor::unselectAllJoints() {