shiritori: remove error

The error was actually checking for an empty 'string' rather than a
empty list of words.

The former would not happen as long as the dictionary of transcription
is valid, and the later is already covered by former winning condition
(WIN_USED).

Author: proppy

functions/shiritori/index.js

@@ -119,9 +119,6 @@ exports.interact = async (dict, word, chain) => {
   // ランダムでえらぶ。
   const w = unused[Math.floor(Math.random() * unused.length)]
   const wk = words[w]
-  if (wk.length === 0) {
-    throw new Error(`no dictionary entry for key: ${w}`)
-  }
   if (wk[wk.length - 1] === 'ん') {
     return { state: exports.state.WIN_N, word: w, kana: wk }
   }

functions/shiritori/test.js

@@ -116,10 +116,3 @@ test('interact: win ん', async t => {
   t.is(result.state, shiritori.state.WIN_N)
   t.is(result.kana[result.kana.length - 1], 'ん')
 })
-
-test('interact: error', async t => {
-  await t.throwsAsync(shiritori.interact(k => Promise.resolve({ 'つけまん': '' }),
-    'とんかつ', ['べんと']),
-  { instanceOf: Error,
-    message: /no dictionary entry/ })
-})