Fix incorrect length check in `DNSName` when extracting qtype or qclass

Fix incorrect length check in `DNSName` when extracting qtype or qclass

In `DNSName::packetParser()`, the length check might have been incorrect
when the caller asked for the `qtype` and/or the `qclass` to be extracted.
The `pos + labellen + 2 > end` check was wrong because `pos` might have already
been incremented by `labellen`. There are 3 ways to exit the main loop:

* `labellen` is 0, the most common case, and in that case the check is valid
* `pos >= end`, meaning that `pos + labellen + 2 > end` will be true regardless
of the value of `labellen` since it cannot be negative
* if `uncompress` is set and a compressed label is found, the main loop is
broken out of, and `labellen` still holds a now irrelevant, possibly non-zero value
corresponding to the first byte of the compressed label length & ~0xc0.

In that last case, if the compressed label points to a position > 255 the check
is wrong and might have rejected a valid packet.
A quick look throught the code didn't show any place where we request decompression
and ask for `qtype` and/or `qclass` in a response, but I might have missed one.

Reported by Houssam El Hajoui (thanks!).