Correction in the documentation of 'io.lines'

The loop does not end on end of file, but when the iterator function
fails to read a value. (In particular, the format "a" never fails,
so a loop with 'io.lines(fname, "a")' never ends.)

liolib.c

@@ -624,7 +624,7 @@ static int io_readline (lua_State *L) {
     lua_pushvalue(L, lua_upvalueindex(3 + i));
   n = g_read(L, p->f, 2);  /* 'n' is number of results */
   lua_assert(n > 0);  /* should return at least a nil */
-  if (lua_toboolean(L, -n))  /* read at least one value? */
+  if (!lua_isnil(L, -n))  /* read at least one value? */
     return n;  /* return them */
   else {  /* first result is nil: EOF or error */
     if (n > 1) {  /* is there error information? */