add texture test

Author: RobertFlatt

Diff for: setup.cfg

@@ -1,6 +1,6 @@
 [metadata]
 name = camera4kivy
-version = 0.2.0
+version = 0.2.1
 author = Robert Flatt
 description = Yet Another Camera for Kivy 
 long_description = file: README.md

Diff for: src/camera4kivy/preview_kivycamera.py

@@ -65,7 +65,7 @@ def on_size(self, instance, size):
         self.canvas.clear()
         if self.error_message:
             self.canvas_text(self.error_message)
-        elif self._camera:
+        elif self._camera and self._camera._texture:
             self.on_tex(None)
         else:
             with self.canvas: