Fix query for unsymbolized frames.
Fix query for unsymbolized frames.

We compared to 0, when it is now NULL.

Change-Id: I2fab076ad48be16959ca0d6055c6090b5d768e31
google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto