apparmor: fixup secid map conversion to using IDR

The IDR conversion did not handle an error case for when allocating a
mapping fails, and it did not ensure that mappings did not allocate or
use a 0 value, which is used as an invalid secid. Which is used when a
mapping fails.

Fixes: 3ae7eb49a2be ("apparmor: Use an IDR to allocate apparmor secids")
Signed-off-by: John Johansen <john.johansen@canonical.com>

security/apparmor/label.c

@@ -407,8 +407,7 @@ bool aa_label_init(struct aa_label *label, int size, gfp_t gfp)
 	AA_BUG(!label);
 	AA_BUG(size < 1);
 
-	label->secid = aa_alloc_secid(label, gfp);
-	if (label->secid == AA_SECID_INVALID)
+	if (aa_alloc_secid(label, gfp) < 0)
 		return false;
 
 	label->size = size;			/* doesn't include null */