perf scripts python: exported-sql-viewer.py: Fix zero id in call graph 'Find' result

perf scripts python: exported-sql-viewer.py: Fix zero id in call graph 'Find' result

Using ctrl-F ('Find') would not find 'unknown' because it matches id zero.
Fix by excluding id zero from selection.

Example:

  $ perf record -e intel_pt//u uname
  Linux
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 0.034 MB perf.data ]
  $ perf script --itrace=bep -s ~/libexec/perf-core/scripts/python/export-to-sqlite.py perf.data.db branches calls
  2020-06-26 15:32:14.928997 Creating database ...
  2020-06-26 15:32:14.933971 Writing records...
  2020-06-26 15:32:15.535251 Adding indexes
  2020-06-26 15:32:15.542993 Dropping unused tables
  2020-06-26 15:32:15.549716 Done
  $ python3 ~/libexec/perf-core/scripts/python/exported-sql-viewer.py perf.data.db

  Select: Reports -> Context-Sensitive Call Graph
  Press: Ctrl-F
  Enter: unknown
  Press: Enter

Before: gets stuck
After: tree is expanded to line showing 'unknown'

Fixes: 254c0d820b86d ("perf scripts python: exported-sql-viewer.py: Factor out CallGraphModelBase")
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: stable@vger.kernel.org
Link: http://lore.kernel.org/lkml/20200629091955.17090-5-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>