tools/bpf_jit_disasm: Fix potential negative tpath index in get_exec_path()

If readlink() fails, len will be -1, which can cause negative indexing
and undefined behavior. This patch ensures that len is set to 0 on
readlink failure, preventing such issues.

Signed-off-by: Ruslan Semchenko <uncleruc2075@gmail.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/r/20250612131816.1870-1-uncleruc2075@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

tools/bpf/bpf_jit_disasm.c

@@ -45,6 +45,8 @@ static void get_exec_path(char *tpath, size_t size)
 	assert(path);
 
 	len = readlink(path, tpath, size);
+	if (len < 0)
+		len = 0;
 	tpath[len] = 0;
 
 	free(path);