demo/get-sequences: Don't fail script when file exists

Useful so that make doesn't tell it has failed while it was just the file that
already existed

demo/get-sequences

@@ -16,4 +16,13 @@ wget -nc -q http://www.vidjil.org/seqs/Stanford_S22.tar.gz
 tar xvzf Stanford_S22.tar.gz
 
 wget -nc -q --show-progress -O LIL-L4.fastq.gz https://db.vidjil.org/vidjil/patient/download/sequence_file.data_file.89a7ad1ac0e2c6fa.4c313530303132352e496f6e5870726573735f3039362e66617374712e677a.gz
+status=$?
+# wget -nc -O exits with 1 when file already exists but thit is is not an
+# error and should not fail the Makefile!
+if [ $status -eq 1 ]; then
+    exit 0
+else
+    exit $status
+fi
+