It already returns whatever strbuf_(grow|addch)() returns in case of
failure, so just return -ENOSPC in the only case where it was die()ing.
When it returns, its only caller will call die() anyway, so no need to
be so eager, die later.

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: http://lkml.kernel.org/n/tip-as05b7mbogprlwi8iarwns8e@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>