[kupfer] plugin.calculator: Fix bug with 0.0 as last result

[Ulrik Sverdrup <usverdrup src gnome org>]

commit ebf6d1142f988bea9a81c6fdde214880cb1bf1e5
Author: Ulrik Sverdrup <ulrik sverdrup gmail com>
Date:   Sun Nov 8 15:38:40 2009 +0100

    plugin.calculator: Fix bug with 0.0 as last result
    
    We should check if self.last_result is None -- else will miss cases
    when the last result evaluates to a false value (0).

 kupfer/plugin/calculator.py |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/kupfer/plugin/calculator.py b/kupfer/plugin/calculator.py
index c9ce934..3bf6f05 100644
--- a/kupfer/plugin/calculator.py
+++ b/kupfer/plugin/calculator.py
@@ -41,7 +41,7 @@ class Calculate (Action):
 		environment = dict(math.__dict__)
 		environment.update(cmath.__dict__)
 		# define some constants missing
-		if self.last_result:
+		if self.last_result is not None:
 			environment["_"] = self.last_result
 		environment["kupfer"] = KupferSurprise("inf")
 		# make the builtins inaccessible