Fix 0 char handling when encoding

The 0 char was encoded as just 0 (as the left->ch == 0 when it is a branch).
Fix is to first compare right index, and if it doesn't match then use last left.

tree.c

@@ -102,14 +102,26 @@ static int write_entry(struct BIT_BUFFER *bitbuf, struct tree *parent,
 		left = parent->left;
 		right = parent->right;
 
-		if (left->ch == c) {
-			int bit = 0;
-			bb_write(bitbuf, &bit, 1);
-			break;
-		} else if (right->ch == c) {
-			int bit = 1;
-			bb_write(bitbuf, &bit, 1);
-			break;
+		if (c != 0) {
+			if (left->ch == c) {
+				int bit = 0;
+				bb_write(bitbuf, &bit, 1);
+				break;
+			} else if (right->ch == c) {
+				int bit = 1;
+				bb_write(bitbuf, &bit, 1);
+				break;
+			}
+		} else {
+			if (left->left == NULL) {
+				int bit = 0;
+				bb_write(bitbuf, &bit, 1);
+				break;
+			} else if (right->ch == c) {
+				int bit = 1;
+				bb_write(bitbuf, &bit, 1);
+				break;
+			}
 		}
 
 		int bit = 0;