PEC: Fix Uninit Var Warning (GCC)

[ax3l]

GCC 13 throws a compile-time warning in 3D that in some cases, is_normal_to_boundary is used as uninitialized. There are a lot of ifs in its usage, so I simply changed the init value to false to silence it.

[dpgrote]

Thanks! I double checked the logic and that variable would have never been used if it was not set. But the fix is good.

[ax3l]

Thanks! Yes, it looks a bit like a noisy compiler diagnostics to me, but the default feels sensible to add.