Add error code for encryption failure in pgcrypto

PXE_DECRYPT_FAILED exists already for decryption errors, and an
equivalent for encryption did not exist.  There is one code path that
deals with such failures for OpenSSL but it used PXE_ERR_GENERIC, which
was inconsistent.  This switches this code path to use the new error
PXE_ENCRYPT_FAILED instead of PXE_ERR_GENERIC, making the code used for
encryption more consistent with the decryption.

Author: Daniel Gustafsson
Discussion: https://postgr.es/m/03049139-CB7A-436E-B71B-42696D3E2EF7@yesql.se

Author: michaelpq

contrib/pgcrypto/openssl.c

@@ -400,7 +400,7 @@ gen_ossl_encrypt(PX_Cipher *c, const uint8 *data, unsigned dlen,
 	}
 
 	if (!EVP_EncryptUpdate(od->evp_ctx, res, &outlen, data, dlen))
-		return PXE_ERR_GENERIC;
+		return PXE_ENCRYPT_FAILED;
 
 	return 0;
 }

contrib/pgcrypto/px.c

@@ -58,6 +58,7 @@ static const struct error_desc px_err_list[] = {
 	{PXE_MCRYPT_INTERNAL, "mcrypt internal error"},
 	{PXE_NO_RANDOM, "Failed to generate strong random bits"},
 	{PXE_DECRYPT_FAILED, "Decryption failed"},
+	{PXE_ENCRYPT_FAILED, "Encryption failed"},
 	{PXE_PGP_CORRUPT_DATA, "Wrong key or corrupt data"},
 	{PXE_PGP_CORRUPT_ARMOR, "Corrupt ascii-armor"},
 	{PXE_PGP_UNSUPPORTED_COMPR, "Unsupported compression algorithm"},

contrib/pgcrypto/px.h

@@ -61,6 +61,7 @@
 #define PXE_MCRYPT_INTERNAL			-16
 #define PXE_NO_RANDOM				-17
 #define PXE_DECRYPT_FAILED			-18
+#define PXE_ENCRYPT_FAILED			-19
 
 #define PXE_PGP_CORRUPT_DATA		-100
 #define PXE_PGP_CORRUPT_ARMOR		-101