FormattedFile::readRecord is slow with std::string

stream/tokenization.h:311 Assertion failed : optr < ochunk.end should be true but was 0

Here's a minimal test case:

(env)mcrusoe@athyra:~/khmer/gl-master$ g++ -I/home/mcrusoe/src/seqan/seqan-1.4.2/core/include/ seqan-std-string-test-1.4.cc -o seqan-std-string-test-1.4 -g
(env)mcrusoe@athyra:~/khmer/gl-master$ g++ -I/home/mcrusoe/src/seqan/seqan-seqan-v2.0.0/include/ seqan-std-string-test-2.0.cc -o seqan-std-string-test-2.0 -g
(env)mcrusoe@athyra:~/khmer/gl-master$ ./seqan-std-string-test-1.4 tests/test-data/random-20-a.fa | head
35      CGCAGGCTGGATTCTAGAGGCAGAGGTGAGCTATAAGATATTGCATACGTTGAGCCAGC
16      CGGAAGCCCAATGAGTTGTCAGAGTCACCTCCACCCCGGGCCCTGTTAGCTACGTCCGT
46      GGTCGTGTTGGGTTAACAAAGGATCCCTGACTCGATCCAGCTGGGTAGGGTAACTATGT
40      GGCTGAAGGAGCGGGCGTACGTGTTTACGGCATGATGGCCGGTGATTATGGGGGACGGG
33      GCAGCGGCTTTGAATGCCGAATATATAACAGCGACGGGGTTCAATAAGCTGCACATGCG
98      ACCAGATGCATAGCCCAACAGCTGAGACATTCCCAGCTCGCGAACCAAGACGTGAGAGC
17      CCCTGTTAGCTACGTCCGTCTAAGGATATTAACATAGTTGCGACTGCGTCCTGTGCTCA
89      GCGAGATACTAGCAAAGGTTCATCAACAGCTACACCCGACGAACCCCGAGAAATTGGGA
30      GTTATGGTCCAGGATGAATGCGCGTACCGGGCGCCTATCACTCCTCTTGTCATTCAGAA
82      ATGCACTATATTTAAGAGGTCTAGAGTGTAAAAAGTGTACCCTTCGGGGTGGAGCTGTT
(env)mcrusoe@athyra:~/khmer/gl-master$ ./seqan-std-string-test-2.0 tests/test-data/random-20-a.fa
/home/mcrusoe/src/seqan/seqan-seqan-v2.0.0/include/seqan/stream/tokenization.h:311 Assertion failed : optr < ochunk.end should be true but was 0
Aborted (core dumped)

Seqan 1.4 version:

#include <seqan/seq_io.h>

int main(int argc, char const ** argv) {
        seqan::SequenceStream _stream;
        seqan::open(_stream, argv[1]);
        std::string name;
        std::string sequence;
        std::string quality;
        while (!seqan::atEnd(_stream)) {
                seqan::readRecord(name, sequence, quality, _stream);
                std::cout << name << '\t' << sequence << '\t' << quality << '\n';
        } 
}

Seqan 2.0 version

#include <seqan/seq_io.h>

int main(int argc, char const ** argv) {
        seqan::SeqFileIn _file;
        seqan::open(_file, argv[1]);
        std::string name;
        std::string sequence;
        std::string quality;
        //seqan::readRecord(name, sequence, _file);
        while (!seqan::atEnd(_file)) {
                seqan::readRecord(name, sequence, quality, _file);
                std::cout << name << '\t' << sequence << '\t' << quality << '\n';
        } 
}

(I ran into this by implementing the Seqan 2.0 changes as recommended by @esiragusa in https://github.com/esiragusa/khmer/commit/66f8c688d74acf06362dc91c35953f6c460c5bba )