Fix missing return value checks

Ensure that all functions have their return values checked where
appropriate. This covers all functions defined and called from within
libssl.

Reviewed-by: Richard Levitte <levitte@openssl.org>
diff --git a/ssl/ssl_rsa.c b/ssl/ssl_rsa.c
index 8799d3d..60a6834 100644
--- a/ssl/ssl_rsa.c
+++ b/ssl/ssl_rsa.c
@@ -693,7 +693,10 @@
         int r;
         unsigned long err;
 
-        SSL_CTX_clear_chain_certs(ctx);
+        if(!SSL_CTX_clear_chain_certs(ctx)) {
+            ret = 0;
+            goto end;
+        }
 
         while ((ca = PEM_read_bio_X509(in, NULL,
                                        ctx->default_passwd_callback,