segment: CDR3/Junction JSON output could be falsely set

When JUNCTIONstart or JUNCTIONend equaled 0, their values
were not modified. But the CDR3/Junction are output in the JSON
as long as the values of the variables are >= 0 (maybe this
should also have been modified). Therefore we could have weird results
with JUNCTIONstart=0 and JUNCTIONend=40.

Tests added.

algo/core/segment.cpp

@@ -1166,8 +1166,11 @@ void FineSegmenter::findCDR3(){
   // There are two cases when we can not detect a JUNCTION/CDR3:
   // - Germline V or J gene has no 'marked_pos'
   // - Sequence may be too short on either side, and thus the backtrack did not find a suitable 'marked_pos'
-  if (JUNCTIONstart == 0 || JUNCTIONend == 0)
+  if (JUNCTIONstart == 0 || JUNCTIONend == 0) {
+    JUNCTIONstart = -1 ;
+    JUNCTIONend = -1 ;    
     return;
+  }
 
   // We require at least two codons
   if (JUNCTIONend - JUNCTIONstart + 1 < 6) {

algo/tests/should-get-tests/no-cdr3-json.should_get

+# The sequences are on TRG, no CDR3 should be found with IGH
+
+!LAUNCH: $VIDJIL_DIR/vidjil $VIDJIL_DEFAULT_OPTIONS -c segment -3 -V $VIDJIL_DIR/germline/IGHV.fa -D $VIDJIL_DIR/germline/IGHD.fa -J $VIDJIL_DIR/germline/IGHJ.fa $VIDJIL_DIR/algo/tests/should-vdj-tests/cdr3-indels.should-vdj.fa; cat out/cdr3-indels.should-vdj.vidjil
+
+$ No CDR3 should be found
+0:TRGV.* [{].*[}]
+
+$ No CDR3 in JSON
+0: "cdr3"
+
+$ No JUNCTION in JSON
+0: "junction"