perf script: Avoid NULL dereference on symbol

al->sym may be NULL given current if conditions and may cause a segv.

Fixes: d2bedb78 ("perf script: Allow --symbol to accept hexadecimal addresses")
Signed-off-by: Ian Rogers <irogers@google.com>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lore.kernel.org/lkml/20200421004329.43109-1-irogers@google.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/event.c

@@ -626,7 +626,7 @@ int machine__resolve(struct machine *machine, struct addr_location *al,
 			ret = strlist__has_entry(symbol_conf.sym_list,
 						al->sym->name);
 		}
-		if (!(ret && al->sym)) {
+		if (!ret && al->sym) {
 			snprintf(al_addr_str, sz, "0x%"PRIx64,
 				al->map->unmap_ip(al->map, al->sym->start));
 			ret = strlist__has_entry(symbol_conf.sym_list,