Update wbemocks.py fix create_text

tests/wbemocks.py

@@ -436,7 +436,10 @@ class MockCanvas:
         else:
             cmd = "create_text: x={} y={} text={}".format(x, y, text)
         self._draw(cmd)
-        y2 = y + font.metrics("linespace")
+        if font is None:
+            y2 = y
+        else:
+            y2 = y + font.metrics("linespace")
         if self._allow("create_text", y2): print(cmd)
 
     def pack(self, expand=None, fill=None):