perf annnotate: Make __symbol__inc_addr_samples handle src->histograms == NULL

Making it a bit more robust, this took place here when a sample appeared
right after:

  ffffffff8a925000 D __nosave_end

And before the next considered symbol, which, using kallsyms make us
over guess the size of __nosave_end, and then the sequence:

  hist_entry__inc_addr_samples ->
    symbol__inc_addr_samples ->
      symbol__hists ->
        annotated_source__alloc_histograms

Ends up not liking to allocate gigabytes of ram for annotation...

This will be alleviated by considering BSS symbols, which we should but
don't so far, and then we should investigate those samples further.

The testcase was to have:

   perf top -e cycles/call-graph=fp/,cache-misses/call-graph=dwarf/,instructions

Running for a while till it segfaulted trying to access NULL notes->src->histograms.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: https://lkml.kernel.org/n/tip-ndfjtpiop3tdcnyjgp320ra8@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>