fix GeometryManager NPE

Initialize geometry manager before registering update observers that involve it,
since the geometry manager's constructor can also trigger them, leading to an
NPE due to the geometryManager field not being set a the time of the call.

See #3. I hope it fixes it :)

Author: garfieldnate

src/main/java/edu/umich/soar/svsviewer/SceneController.java

@@ -71,6 +71,9 @@ public class SceneController {
 
   @FXML
   public void initialize() {
+    this.geometryManager =
+        new GeometryManager(preferences, rootPane, shapeGroup, this::showMessage);
+
     // TODO: would prefer to bind in the FXML file, but I couldn't get that to work.
     viewerScene.heightProperty().bind(rootPane.heightProperty());
     viewerScene.widthProperty().bind(rootPane.widthProperty());
@@ -174,9 +177,6 @@ public void initialize() {
 
     rerenderSceneOnChange(rootGroup.boundsInParentProperty());
 
-    this.geometryManager =
-        new GeometryManager(preferences, rootPane, shapeGroup, this::showMessage);
-
     Consumer<String> inputProcessor =
         (String line) -> {
           List<String> tokens = Tokenizer.tokenizeCommand(line);