Fix no return

Just return 0 as I will not bother moving these to void

header.c

@@ -62,7 +62,7 @@ static int read_entry(struct BIT_BUFFER *bitbuf, struct tree *parent)
 
 static int read_entries(struct BIT_BUFFER *bitbuf, struct tree *parent)
 {
-	read_entry(bitbuf, parent);
+	return read_entry(bitbuf, parent);
 }
 
 int decode_header(struct BIT_BUFFER *bitbuf, struct tree *parent)

huffman.c

@@ -106,6 +106,8 @@ static int encode_file(FILE *in, FILE *out)
 	free_tree(tree);
 
 	bb_flush(&bitbuf);
+
+	return 0;
 }
 
 static int decode_file(FILE *in, FILE *out)

tree.c

@@ -179,6 +179,7 @@ static int write_entry(struct BIT_BUFFER *bitbuf, struct tree *parent,
 	for (int i = length-1; i >= 0; i--) {
 		bb_write(bitbuf, &pathbuf[i], 1);
 	}
+	return 0;
 }
 
 int encode_tree(struct BIT_BUFFER *bitbuf, struct tree *parent, char *buf,