Any pie fillings that are particularly saucy can add extra moisture to the bottom layer of pastry, making it limp and soft. The creamy chicken and bacon mixture in this pie is no exception. However, you can avoid a 'soggy bottom' through a technique called blind baking.
Blind baking might sound a little strange, but it's actually very straightforward. It simply involves baking the pastry a little (around 15 minutes for puff pastry) before you add the filling and then return to the oven to fully bake it.
There are a few things that are needed for this method to be successful. Firstly make sure that you have lined the pie dish as closely as possible with the pastry. Press the pastry in carefully around the edges and corners. Secondly line the pastry inside the dish with some baking/parchment paper. Then you need to add some weight to the bottom of the dish which will stop the pastry from rising. You can buy ready-made baking beads which are actually made for exactly this purpose, or you can use some uncooked rice instead (but you'll need to throw it away after so it is a little wasteful).