fix KmerUtil.mergeTwoKmer bug while merging 1byte nextKmer

git-svn-id: https://hyracks.googlecode.com/svn/branches/fullstack_genomix@3371 123451ca-8445-de46-9d55-352943316053
diff --git a/genomix/genomix-data/src/main/java/edu/uci/ics/genomix/type/KmerUtil.java b/genomix/genomix-data/src/main/java/edu/uci/ics/genomix/type/KmerUtil.java
index 7982c14..d796d19 100644
--- a/genomix/genomix-data/src/main/java/edu/uci/ics/genomix/type/KmerUtil.java
+++ b/genomix/genomix-data/src/main/java/edu/uci/ics/genomix/type/KmerUtil.java
@@ -158,7 +158,9 @@
 		for (; i <= kmerPre.length; i++) {
 			mergedKmer[byteNum - i] = kmerPre[kmerPre.length - i];
 		}
-		i--;
+		if ( i > 1){
+			i--;
+		}
 		if (preK % 4 == 0) {
 			for (int j = 1; j <= kmerNext.length; j++) {
 				mergedKmer[byteNum - i - j] = kmerNext[kmerNext.length - j];