fix($http): don't run transformData on HEAD methods

[tbosch]

7b6c1d0 created this issue by using Content-Type to
determine when to run fromJson. Because HEAD methods do not contain
a body but are supposed to return the Content-Type header that would
have been returned if it was a GET this functionality fails.

Closes #9528

[mary-poppins]

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[IgorMinar]

There is a related issue: #9532 which describes the same kind of error because server responded with HTTP 204 No Content.

We should change the PR to simply not parse the response if it's empty.

[tbosch]

Haven't seen your comment, will create a new PR for #9532