fixing possible exception when reading SCF files

occurs when reading SCF files without comments or private data

Signed-off-by: Hannes Brandstätter-Müller <hannes.mueller@gmail.com>

sequencing/src/main/java/org/biojava/bio/program/scf/SCF.java

@@ -361,8 +361,12 @@ public void parse() throws IOException,
             TreeMap sectionOrder = new TreeMap();
             sectionOrder.put(new Long(header.samples_offset),  SAMPLES);
             sectionOrder.put(new Long(header.bases_offset),    BASES);
-            sectionOrder.put(new Long(header.comments_offset), COMMENTS);
-            sectionOrder.put(new Long(header.private_offset),  PRIVATE);
+            if (header.comments_size > 0) {
+                sectionOrder.put(new Long(header.comments_offset), COMMENTS);
+            }
+            if (header.private_size > 0) {
+                sectionOrder.put(new Long(header.private_offset), PRIVATE);
+            }
 
             for (Iterator it = sectionOrder.keySet().iterator() ;
             it.hasNext() ;) {