InDetTrackHoleSearch: Fix cppcheck warning.

Protect against potential null pointer dereference.

This merge request affects 1 package:

• InnerDetector/InDetRecTools/InDetTrackHoleSearch

Adding @goetz ,@oda ,@amorley ,@sroe as watchers

added InnerDetector master review-pending-level-1 labels

CI Result SUCCESS (hash c9fb9e14)

	Athena	AthSimulation	AnalysisBase	AthGeneration
externals
cmake
make
required tests
optional tests

Full details available on this CI monitor view
Athena: number of compilation errors 0, warnings 0
AthSimulation: number of compilation errors 0, warnings 0
AnalysisBase: number of compilation errors 0, warnings 0
AthGeneration: number of compilation errors 0, warnings 0
For experts only: Jenkins output [CI-MERGE-REQUEST-CC7 12484]

merged

mentioned in commit bf98370e

added sweep:ignore label