Bug 1177476 - Fix require_conditions regression in mach, r=gps

This is a regression from bug 1176620 that results in all Firefox mach commands showing up in the help for B2G, even though they don't work there.

--HG--
extra : rebase_source : e779b866a82c2df1dbf913d24b93a0dc9838ff9f

python/mach/mach/decorators.py

@@ -144,7 +144,7 @@ def CommandProvider(cls):
 
         seen_commands.add(command.name)
 
-        if command.conditions is None and Registrar.require_conditions:
+        if not command.conditions and Registrar.require_conditions:
             continue
 
         msg = 'Mach command \'%s\' implemented incorrectly. ' + \