Add null check to SQLiteConnectionPool.dump()

This change adds a null check before adding the current connection
pool path's parent to the list of directories, since the parent might be
null. This avoids an NPE in SQLiteDatabase.dumpAll().

Test: run dumpsys dbinfo, verify that it no longer times out
Bug: 281043011
Change-Id: Iec7fa9d0941d79dfa034f117c35c30797c7d3113