Fix the following error if shrink / enlarge font is used with the help
window.

  Traceback (most recent call last):
    File "tools/perf/scripts/python/exported-sql-viewer.py", line 2791, in ShrinkFont
      ShrinkFont(win.view)
  AttributeError: 'HelpWindow' object has no attribute 'view'

Committer testing:

Before, matches above output:

  $ python ~acme/libexec/perf-core/scripts/python/exported-sql-viewer.py ~/c/adrian.hunter/simple-retpoline.db
  Traceback (most recent call last):
    File "/home/acme/libexec/perf-core/scripts/python/exported-sql-viewer.py", line 2780, in EnlargeFont
      EnlargeFont(win.view)
  AttributeError: 'HelpWindow' object has no attribute 'view'
  $

After:

No more tracebacks, but the fonts don't get enlarged, which is kinda
frustrating...
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: http://lkml.kernel.org/r/20190503120828.25326-2-adrian.hunter@intel.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>