fix ReadVarSize bug

bin.go

@@ -1022,9 +1022,10 @@ func ReadVarSize(src io.ByteReader) (_ int, err error) {
 		if err != nil {
 			return
 		}
+
 		if b >= 128 {
 			num |= uint64(b&127) << uint(i*7)
-			return
+			return int(num), nil
 		}
 		num |= uint64(b) << uint(i*7)
 	}