The existing Decoder.tokenError implementation creates its error messages by
concatenating "invalid character " + quoteChar(c) + " " + context. All context
values however already start with a space leading to error messages containing
two spaces.

This change removes " " from the concatenation expression.

Fixes #26587

Change-Id: I93d14319396636b2a40d55053bda88c98e94a81a
GitHub-Last-Rev: 6db7e1991b15beee601f558be72a2737070d8f68
GitHub-Pull-Request: golang/go#26588
Reviewed-on: https://go-review.googlesource.com/125775Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>