RFR: 8257707: Fix incorrect format string in Http1HeaderParser

[Aleksey Shipilev]

On Fri, 4 Dec 2020 08:36:36 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> Incorrect format string was found by IntelliJ IDEA inspection `Java | Probable bugs | Malformed format string`
>
> Looks good to me.

@dfuch, are you still good with this? Please submit your formal review here :)

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PR: https://git.openjdk.java.net/jdk/pull/1495