fix potential bug with count based collocation window

Change-Id: Icb1dbc29c0c287c71f7b295e3b397d6d10bc5a85
diff --git a/src/dereko2vec.c b/src/dereko2vec.c
index 9e9c02e..0bc021c 100644
--- a/src/dereko2vec.c
+++ b/src/dereko2vec.c
@@ -1685,7 +1685,7 @@
 					}
 			}
 		} else if(type == 5) {
-			for (a = b; a < window * 2 + 1 - b; a++) if (a != window) {
+			for (a = 0; a < window * 2 + 1 - b; a++) if (a != window) {
 				c = sentence_position - window + a;
 				if (c < 0) continue;
 				if (c >= sentence_length) continue;