fix error found by coverity: check if ctx is != NULL before calling BN_CTX_end()

crypto/dh/dh_key.c

@@ -217,8 +217,11 @@ static int compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh)
 
 	ret=BN_bn2bin(tmp,key);
 err:
-	BN_CTX_end(ctx);
-	BN_CTX_free(ctx);
+	if (ctx != NULL)
+		{
+		BN_CTX_end(ctx);
+		BN_CTX_free(ctx);
+		}
 	return(ret);
 	}
 

crypto/ec/ec2_smpl.c

@@ -281,7 +281,8 @@ int ec_GF2m_simple_group_check_discriminant(const EC_GROUP *group, BN_CTX *ctx)
 	ret = 1;
 
 err:
-	BN_CTX_end(ctx);
+	if (ctx != NULL)
+		BN_CTX_end(ctx);
 	if (new_ctx != NULL)
 		BN_CTX_free(new_ctx);
 	return ret;

crypto/ec/ec_check.c

@@ -113,7 +113,8 @@ int EC_GROUP_check(const EC_GROUP *group, BN_CTX *ctx)
 	ret = 1;
 
 err:
-	BN_CTX_end(ctx);
+	if (ctx != NULL)
+		BN_CTX_end(ctx);
 	if (new_ctx != NULL)
 		BN_CTX_free(new_ctx);
 	if (point)

crypto/ec/ecp_smpl.c

@@ -336,7 +336,8 @@ int ec_GFp_simple_group_check_discriminant(const EC_GROUP *group, BN_CTX *ctx)
 	ret = 1;
 
 err:
-	BN_CTX_end(ctx);
+	if (ctx != NULL)
+		BN_CTX_end(ctx);
 	if (new_ctx != NULL)
 		BN_CTX_free(new_ctx);
 	return ret;

crypto/rsa/rsa_gen.c

@@ -183,8 +183,11 @@ err:
 		RSAerr(RSA_F_RSA_BUILTIN_KEYGEN,ERR_LIB_BN);
 		ok=0;
 		}
-	BN_CTX_end(ctx);
-	BN_CTX_free(ctx);
+	if (ctx != NULL)
+		{
+		BN_CTX_end(ctx);
+		BN_CTX_free(ctx);
+		}
 
 	return ok;
 	}