People universally read more into the Roman Catechism passage than what it's actually saying.
It's saying that infants should be baptized without undue delay, since there's a danger that they might die without the Sacrament and be lost.
On the contrary, for adults, their proper dispositions to receive the Sacrament will avail them to grace. All this is saying is that God will grant their desires (seek and you shall find) ... and prevent them from being cut off by some misfortune from receiving the grace they desired, i.e. justification through Baptism. This does NOT state that if they died at that moment they would be saved.
Now the confusion comes from that phrase "should any unforeseen misfortune ..." actually has the sense in Latin of "lest any unforseen accident".
St. Rufinus, a Church Father, used this exact language (at least in translation, since I don't have the Latin), when he said that a man's confession of the faith will avail him to justification ... and then added the phrase, so that he would be ensured of receiving Baptism. In other words, the meaning there ... and this passage in Trent clearly echos St. Rufinus ... was that once you have the proper dispositions for Baptism, God will MAKE SURE YOU GET IT.
It's similar to the speculations of St. Ambrose that are universally misinterpreted as an endorsement of BoD. St. Ambrose said that Valentinian received the grace that he sought. Ask and you shall receive. Whatever it is that he desired and sought, he received. Could he have been given an emergency Baptism? Either that, or he received what he asked for, the implication being that if he did not receive Baptism, it was because he did not properly will to receive it. That's all St. Ambrose was saying there, and all that the Roman Catechism is saying here, and what St. Rufinus explicitly taught. This passage falls short of an endorsement of BoD, although it does leave the question open. St. Ambrose, in other writings, explicitly rejects the possibility that a catechumen who dies before Baptism can be saved. So it would not make sense to read the Valentinian passage as a sudden about-face endorsement of BoD.