Protect from an NPE if we find no graphics yet at sprite initialization time.

git-svn-id: svn+ssh://src.earth.threerings.net/nenya/trunk@106 ed5b42cb-e716-0410-a449-f6a68f950b19

src/java/com/threerings/media/sprite/ButtonSprite.java

@@ -255,10 +255,12 @@ public class ButtonSprite extends Sprite
         // lay out the label if not already
         if (!_label.isLaidOut()) {
             Graphics2D gfx = _mgr.createGraphics();
-            try {
-                _label.layout(gfx);
-            } finally {
-                gfx.dispose();
+            if (gfx != null) {
+                try {
+                    _label.layout(gfx);
+                } finally {
+                    gfx.dispose();
+                }
             }
         }