encoding/json: eliminate superfluous space in Decoder.Token error messages

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>

src/encoding/json/stream.go

@@ -471,7 +471,7 @@ func (dec *Decoder) tokenError(c byte) (Token, error) {
 	case tokenObjectComma:
 		context = " after object key:value pair"
 	}
-	return nil, &SyntaxError{"invalid character " + quoteChar(c) + " " + context, dec.offset()}
+	return nil, &SyntaxError{"invalid character " + quoteChar(c) + context, dec.offset()}
 }
 
 // More reports whether there is another element in the