cljs.core.specs.alpha: Check early if let binding vector is even

Description

When is applied, port it to ClojureScript.

This line can be updated to match the revision in the patch in CLJ-2376:
https://github.com/clojure/clojurescript/blob/17b71461ee6304e3696e397add1f4780525553fc/src/main/cljs/cljs/core/specs/alpha.cljc#L59

Environment

None

Assignee

Unassigned

Reporter

Mike Fikes

Labels

Approval

None

Patch

None

Priority

Minor
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