add NaN protection to HSGN2 photon decorations

This MR adds a simple check to the experimental HSGN2 PV selection algorithm to protect against very rare downstream crashes when a NaN is assigned during the photon pointing decorations.

@jburzyns @hhanif @gfrattar

This merge request affects 1 package:

• InnerDetector/InDetRecTools/InDetGNNHardScatterSelection

This merge request affects 1 file:

• InnerDetector/InDetRecTools/InDetGNNHardScatterSelection/src/VertexDecoratorAlg.cxx

Adding @sroe ,@goetz as watchers

added InnerDetector main review-pending-level-1 labels

CI Result SUCCESS (hash 83936d52)

	Athena
externals
cmake
make
tests

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Changes seem fine to me. Approving from L1 side (Fábio).

removed review-pending-level-1 label

added review-approved label

merged

mentioned in commit 28194f29