update the check of feature flag

[geetha-1z]

Updating the feature flag check to return false if it's not present
The previous code is failing to check the feature flag and here is the issue
PolypressRegistry.namespace([:polypress, :paper_notices]).feature_enabled?(:upload_paper_notices_to_s3)[10:40 AM]irb(main):003:0> PolypressRegistry.namespace([:polypress, :paper_notices]).feature_enabled?(:upload_paper_notices_to_s3)Traceback (most recent call last):    2: from (irb):2    1: from (irb):3:in rescue in irb_binding'NoMethodError (undefined method arity' for nil:NilClass)

The updated code which is in this PR shows below results in the console

PVT
irb(main):001:0> PolypressRegistry.feature_enabled?(:upload_paper_notices_to_s3)
=> true
PVT-3
irb(main):001:0> PolypressRegistry.feature_enabled?(:upload_paper_notices_to_s3)
=> false