Clear error queue when starting SSL_CTX_use_certificate_chain_file

PR: 1417, 1513
Submitted by: Erik de Castro Lopo <mle+openssl@mega-nerd.com>

ssl/ssl_rsa.c

@@ -708,6 +708,12 @@ int SSL_CTX_use_certificate_chain_file(SSL_CTX *ctx, const char *file)
 	int ret=0;
 	X509 *x=NULL;
 
+	ERR_clear_error(); /* This function needs to check the error stack
+			      even if the return code(s) of called functions
+			      indicate success.
+			      The error stack must therefore be cleared
+			      before starting. */
+
 	in=BIO_new(BIO_s_file_internal());
 	if (in == NULL)
 		{