EAP-FAST: Make PAC file A_ID parser easier to analyze

Some static analyzers seem to have issues with "pos + len > end"
validation (CID 62875), so convert this to "len > end - pos" to make it
more obvious that len is validated against its bounds.

Signed-off-by: Jouni Malinen <j@w1.fi>

src/eap_peer/eap_fast_pac.c

@@ -714,7 +714,7 @@ static void eap_fast_pac_get_a_id(struct eap_fast_pac *pac)
 		pos += 2;
 		len = WPA_GET_BE16(pos);
 		pos += 2;
-		if (pos + len > end)
+		if (len > (unsigned int) (end - pos))
 			break;
 
 		if (type == PAC_TYPE_A_ID) {