Return error 400 if path part is invalid instead of 500

[gugu]

Current behaviour:
curl corp.short.cm/%AF returns 500 Internal Server Error
Expected:
curl corp.short.cm/%AF returns 400 Invalid request

I'm running a link shortener service and user put different combinations in path part, some of them are valid, some of them - not. This case I sent is a client error and there is no need to raise an exception here

URIError: URI malformed
  ?, in decodeURIComponent
  File "/srv/shorturl_redirector/node_modules/koa-route/index.js", line 60, col 19, in decode
    if (val) return decodeURIComponent(val);
  ?, in Array.map
  File "/srv/shorturl_redirector/node_modules/koa-route/index.js", line 34, col 35, in null.<anonymous>
    const args = m.slice(1).map(decode);
  File "/srv/shorturl_redirector/node_modules/koa-compose/index.js", line 42, col 32, in dispatch
    return Promise.resolve(fn(context, dispatch.bind(null, i + 1)));
  File "/srv/shorturl_redirector/node_modules/koa-route/index.js", line 43, col 16, in null.<anonymous>
    return next();
  File "/srv/shorturl_redirector/node_modules/koa-compose/index.js", line 42, col 32, in dispatch
    return Promise.resolve(fn(context, dispatch.bind(null, i + 1)));
  File "/srv/shorturl_redirector/node_modules/koa-route/index.js", line 43, col 16, in null.<anonymous>
    return next();
  File "/srv/shorturl_redirector/node_modules/koa-compose/index.js", line 42, col 32, in dispatch
    return Promise.resolve(fn(context, dispatch.bind(null, i + 1)));
  File "/srv/shorturl_redirector/node_modules/koa-route/index.js", line 43, col 16, in null.<anonymous>
    return next();
  File "/srv/shorturl_redirector/node_modules/koa-compose/index.js", line 42, col 32, in dispatch
    return Promise.resolve(fn(context, dispatch.bind(null, i + 1)));
  File "/srv/shorturl_redirector/node_modules/koa-route/index.js", line 43, col 16, in null.<anonymous>
    return next();
  File "/srv/shorturl_redirector/node_modules/koa-compose/index.js", line 42, col 32, in dispatch
    return Promise.resolve(fn(context, dispatch.bind(null, i + 1)));
  File "/srv/shorturl_redirector/node_modules/koa-route/index.js", line 43, col 16, in null.<anonymous>
    return next();
  File "/srv/shorturl_redirector/node_modules/koa-compose/index.js", line 42, col 32, in dispatch
    return Promise.resolve(fn(context, dispatch.bind(null, i + 1)));
  File "/srv/shorturl_redirector/node_modules/koa-views/src/index.js", line 55, col 12, in views
    return next()
  File "/srv/shorturl_redirector/node_modules/koa-compose/index.js", line 42, col 32, in dispatch
    return Promise.resolve(fn(context, dispatch.bind(null, i + 1)));
  File "/srv/shorturl_redirector/node_modules/koa-body/index.js", line 110, col 14, in null.<anonymous>
    return next();
  File "internal/process/next_tick.js", line 68, col 7, in process._tickCallback