Fix NinePatch.initialize (#2615)

The initialized test was reversed

Author: einarf

arcade/gui/nine_patch.py

@@ -123,7 +123,7 @@ def initialize(self) -> None:
         Manually initialize the NinePatchTexture if it was lazy loaded.
         This has no effect if the NinePatchTexture was already initialized.
         """
-        if self._initialized:
+        if not self._initialized:
             self._init_deferred()
 
     @property