perf dlfilter: Be defensive against potential NULL dereference

In the unlikely case of having a symbol without a mapping, avoid a
NULL dereference that clang-tidy warns about.

Signed-off-by: Ian Rogers <[e-mail]>
Acked-by: Namhyung Kim <[e-mail]>
Cc: Ravi Bangoria <[e-mail]>
Cc: Nick Desaulniers <[e-mail]>
Cc: Yang Jihong <[e-mail]>
Cc: Huacai Chen <[e-mail]>
Cc: Nathan Chancellor <[e-mail]>
Cc: Kan Liang <[e-mail]>
Cc: [e-mail]
Cc: Ming Wang <[e-mail]>
Cc: Tom Rix <[e-mail]>
Cc: [e-mail]
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Namhyung Kim <[e-mail]>

tools/perf/util/dlfilter.c

···
 		d_al->sym_end = sym->end;
 		if (al->addr < sym->end)
 			d_al->symoff = al->addr - sym->start;
-		else
+		else if (al->map)
 			d_al->symoff = al->addr - map__start(al->map) - sym->start;
+		else
+			d_al->symoff = 0;
 		d_al->sym_binding = sym->binding;
 	} else {
 		d_al->sym = NULL;