defaults in alternatives with a match mode set are not returned

[nlundquist]

Support plan

• is this issue currently blocking your project? (yes/no): yes
• is this issue affecting a production system? (yes/no): no

Context

• node version: 12.x
• module version with issue: 17.3.0
• last module version without issue: n/a
• environment (e.g. node, browser, native): node
• used with (e.g. hapi application, another framework, standalone, ...): standalone

What are you trying to achieve or the steps to reproduce?

Properties with defaults should be applied, even if they're part of an alternative subschema with a match mode.

const joi = require('joi')
const s = joi.alternatives().try(
  joi.object({ 
    lol: joi.string().default('rofl')
  }).unknown(), 
  joi.object({ 
    foo: joi.string().default('bar'), 
    baz: joi.string() 
  })
).match('all')
const { value, error } = s.validate({ baz: 'bing' })

What was the result you got?

error === undefined
value === { baz: 'bing' }

What result did you expect?

error === undefined
value === { lol: 'rofl', foo: 'bar', baz: 'bing' }

[nlundquist]

Could you take a look at this when you have a chance @hueniverse ?

Have some work that depends on this and would appreciate any help getting this into a release so I can get off my fork.