move valid check to beginning of loop

[bendavies]

I'm seeing an issue with a CSV I have where this line
https://github.com/portphp/csv/blob/master/src/CsvReader.php#L116
is coming back as false on the last line.
Switching the do while to a while loop fixes this, but I can't work out why it's happening or replicate it in a test.

Anyway, it doesn't break any existing tests.

[rodnaph]

This fixes an issue I'm having trying to use CsvReader with the OneToManyReader 👍

[slashrsm]

Superseded by #18 — same do-while → while ($this->valid()) change, with a reproducible test.

Root cause

SplFileObject::current() returns false at EOF. With headers set, the old do { $line = $this->file->current(); … count($line) … } while ($this->valid()) still entered the body once when the iterator was already invalid → count(false) TypeError on PHP 8+.

Why a plain last-line CSV never failed in tests

Foreach only calls current() when valid() is true, so normal “last data line” fixtures never hit the bad path.

What does hit it

Port\Reader\OneToManyReader (as @rodnaph noted) calls rightReader->current() after next() past the last detail row. Also: current() / getRow() after the reader is exhausted.

Please close this PR in favor of #18 once that lands. Thanks for the original diagnosis — the loop change was correct.

[slashrsm]

Closed as superseded by #18 (merged).