Update falcon.c

In some case, if there is a big alignment gap > UINT8_MAX, without this line, it will segfault as we don't except gaps that larger.  This is safety guard.  The sequence alignment should not generate such gap before sending it to this function.

src/c/falcon.c

@@ -147,6 +147,8 @@ align_tags_t * get_align_tags( char * aln_q_seq,
             p_j = j;
             p_jj = jj;
             p_q_base = aln_q_seq[k];
+        } else {
+            break; // when there is a big alignment gap > UINT8_MAX, stop to extned the tagging string
         }
     }
     // sentinal at the end