perf report/top: Do not offer annotation for symbols without samples

This can happen in the --children mode, i.e. the default mode when
callchains are present, where one of the main entries may be a callchain
entry with no samples.

So far we were not providing any information about why an annotation
couldn't be provided even offering the Annotation option in the popup
menu.

Work is needed to allow for no-samples "annotation', i.e. to show the
disassembly anyway and allow for navigation, etc.

Reviewed-by: Jiri Olsa <jolsa@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jin Yao <yao.jin@linux.intel.com>
Cc: Kan Liang <kan.liang@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lkml.kernel.org/n/tip-0hhzj2de15o88cguy7h66zre@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>