Crash on input containing single read

[KirillKryukov]

DSRC crashes when trying to compress a file containing a single read. For example:

@1
TAACGAAACCGGCATGGAACCTCCTGTTNTTGTGGCGGGGGGGGGTAGGCTAGAGAGCTGGCGCCCGCAACCCGGGGGGGGACTTTNNNGGGGGGGGCGG
+
IIHHIIIIIIIIIHIDEGHIIIIIIFEE#CEEA###################################################################

The read looks ordinary to me. I also tried other reads with the same effect.

Full steps to reproduce:

cd /tmp
mkdir dsrc-repro-2
cd dsrc-repro-2
git clone https://github.com/refresh-bio/DSRC
cd DSRC
make -f Makefile.c++11 bin
cd ..
wget http://kirill.med.u-tokai.ac.jp/data/temp/dsrc-repro-2.fastq
./DSRC/bin/dsrc c -d0 -q0 -b8 -t1 dsrc-repro-2.fastq dsrc-repro-2.dsrc

Test machine: Ubuntu 18.04.1 LTS, dual Xeon E5-2643v3.

DSRC crashes with this output:

terminate called after throwing an instance of 'dsrc::DsrcException'
  what():  Error analyzing FASTQ dataset
Aborted (core dumped)

[KirillKryukov]

This could be related to Issue #21 .