Exclude identities when PERCENTAGE_SPLIT trait is undefined

[emyller]

Users without specified trait appear in segment, evaluated using identity key instead.

Acceptance criteria

• Return false when trait is undefined instead of falling back to identity key

Current implementation:

flagsmith-ruby-client/lib/flagsmith/engine/segments/evaluator.rb

Line 160 in 5ddd02d

context_value_key = get_context_value(condition[:property], context) || get_identity_key_from_context(context)

See Flagsmith/flagsmith-engine#283 for context.