coverity issue 394701 possible derefernce before null check

wolfcrypt/src/rsa.c

@@ -673,13 +673,17 @@ static int _ifc_pairwise_consistency_test(RsaKey* key, WC_RNG* rng)
 
 int wc_CheckRsaKey(RsaKey* key)
 {
- DECL_MP_INT_SIZE_DYN(tmp, mp_bitsused(&key->n), RSA_MAX_SIZE);
 #ifdef WOLFSSL_SMALL_STACK
  WC_RNG *rng = NULL;
 #else
  WC_RNG rng[1];
 #endif
  int ret = 0;
+ DECL_MP_INT_SIZE_DYN(tmp, (key)? mp_bitsused(&key->n) : 0, RSA_MAX_SIZE);
+
+ if (key == NULL) {
+ return BAD_FUNC_ARG;
+ }
 
 #ifdef WOLFSSL_CAAM
  /* can not perform these checks on an encrypted key */
@@ -711,11 +715,6 @@ int wc_CheckRsaKey(RsaKey* key)
  ret = MP_INIT_E;
  }
 
- if (ret == 0) {
- if (key == NULL)
- ret = BAD_FUNC_ARG;
- }
-
  if (ret == 0)
  ret = _ifc_pairwise_consistency_test(key, rng);