fix: allow NaN in schema describe() output validation

When a schema includes .allow(NaN), calling .describe() would throw a
ValidationError because NaN was not listed as a valid item type in the
internal manifest values schema.

NaN is a valid JavaScript number and a legitimate value to allow in a
joi schema. The fix adds NaN alongside the existing Infinity and
-Infinity exceptions in the internals.desc.values definition.

Fixes #3094

Author: ordinary9843

lib/schemas.js

@@ -210,7 +210,7 @@ internals.desc.values = Joi.array()
         null,
         Joi.boolean(),
         Joi.function(),
-        Joi.number().allow(Infinity, -Infinity),
+        Joi.number().allow(Infinity, -Infinity, NaN),
         Joi.string().allow(''),
         Joi.symbol(),
         internals.desc.buffer,

test/manifest.js

@@ -254,6 +254,15 @@ describe('Manifest', () => {
             expect(Joi.invalid(1).allow(1).describe()).to.equal({ type: 'any', allow: [1] });
         });
 
+        it('handles NaN in allow list', () => {
+
+            const schema = Joi.number().allow(NaN);
+            const desc = schema.describe();
+            expect(desc.type).to.equal('number');
+            expect(desc.allow).to.have.length(1);
+            expect(Number.isNaN(desc.allow[0])).to.equal(true);
+        });
+
         it('describes ruleset changes', () => {
 
             const schema = Joi.string().min(1).keep();