Check count for 'not None' instead of truthy in command decorator

The command decorator was only checking the truthyness of `count`, which
meant that a value of 0 was considered falsy and so the value not passed
to the decorated function. A value of 0 for `count` should be valid
since this is the default in both vim and neovim (see `help v:count`).

Author: malramsay64

neovim/plugin/decorators.py

@@ -55,7 +55,7 @@ def dec(f):
 
         if range is not None:
             opts['range'] = '' if range is True else str(range)
-        elif count:
+        elif count is not None:
             opts['count'] = count
 
         if bang: