util.poll: Add missing return statements in fallback mode

These allowed modifying or deleting select() state for unregistered FDs.
During normal usage this should never happen. Modifying one that isn't
set might cause weirdness but deleting an already deleted FD isn't a
problem.

util-src/poll.c

@@ -172,6 +172,7 @@ static int Lset(lua_State *L) {
 		lua_pushnil(L);
 		lua_pushstring(L, strerror(ENOENT));
 		lua_pushinteger(L, ENOENT);
+		return 3;
 	}
 
 	if(!lua_isnoneornil(L, 3)) {
@@ -229,6 +230,7 @@ static int Ldel(lua_State *L) {
 		lua_pushnil(L);
 		lua_pushstring(L, strerror(ENOENT));
 		lua_pushinteger(L, ENOENT);
+		return 3;
 	}
 
 	FD_CLR(fd, &state->wantread);