Avoid crashing when a directory does not exist

This change adds a null-check for the DIR* object to avoid a crash when
the directory cannot be opened for any reason.

(cherrypick of d0512717)

Bug: 74568776
Test: calling dumpstate early in the boot sequence no longer crashes
Change-Id: I6c80f38dcf7890e607ce73e25a8ec0e16ba92586
Merged-In: I6c80f38dcf7890e607ce73e25a8ec0e16ba92586