/share gives raises a js exception on v2.1.0rc3

[renatolond]

Using /share?text= with any content raises a javascript exception which makes impossible to share.

Uncaught TypeError: Cannot read property 'a' of undefined
    at r (configureStore.js:9)
    at Object.<anonymous> (mastodon.js:18)
    at t (bootstrap 62e727d2c158d7906cb8:54)
    at Object.<anonymous> (common-79da9261df3f2d141a5e.js:20599)
    at t (bootstrap 62e727d2c158d7906cb8:54)
    at Object.<anonymous> (common-79da9261df3f2d141a5e.js:17843)
    at t (bootstrap 62e727d2c158d7906cb8:54)
    at Object.<anonymous> (common-79da9261df3f2d141a5e.js:33014)
    at t (bootstrap 62e727d2c158d7906cb8:54)
    at Object.<anonymous> (common-79da9261df3f2d141a5e.js:27028)
    at t (bootstrap 62e727d2c158d7906cb8:54)
    at Object.<anonymous> (common-79da9261df3f2d141a5e.js:14713)
    at t (bootstrap 62e727d2c158d7906cb8:54)
    at Object.660 (share-9d786f471d63e1846ee7.js:4912)
    at t (bootstrap 62e727d2c158d7906cb8:54)
    at HTMLDocument.o (share.js:6)

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• I searched or browsed the repo’s other issues to ensure this is not a duplicate.
• This bug happens on a tagged release and not on master (If you're a user, don't worry about this).

[ykzts]

resolved with #5941.