bugfix: remove sslhandshake result assert for pre-handshake errors. (#534)

When `tcpsock:sslhandshake()` fails before the actual SSL handshake starts,
`ngx_http_lua_ffi_socket_tcp_get_sslhandshake_result()` may return `FFI_OK`
while still providing the OpenSSL error details.

One example is a client private key setup failure. In that path, `rc` is
`FFI_ERROR`, but `u->error_ret` is not set,
so `ngx_http_lua_ffi_socket_tcp_get_sslhandshake_result` would return `FFI_OK`.
The existing `assert(res == FFI_ERROR)` turns this expected
error-reporting path into an assertion failure.

This patch removes the assertion so Lua can return the original SSL error to
the caller.

Author: tzssangglass

lib/resty/core/socket.lua

@@ -424,14 +424,10 @@ local function sslhandshake(cosocket, reused_session, server_name, ssl_verify,
         error("no request ctx found", 2)
     end
 
-    local res
-
     if rc == FFI_ERROR then
-        res = C.ngx_http_lua_ffi_socket_tcp_get_sslhandshake_result(r, u,
+        C.ngx_http_lua_ffi_socket_tcp_get_sslhandshake_result(r, u,
                   session_ptr, errmsg, openssl_error_code)
 
-        assert(res == FFI_ERROR)
-
         if openssl_error_code[0] ~= 0 then
             return nil, openssl_error_code[0] .. ": " .. ffi_str(errmsg[0])
         end
@@ -443,6 +439,8 @@ local function sslhandshake(cosocket, reused_session, server_name, ssl_verify,
         return reused_session
     end
 
+    local res
+
     if rc == FFI_OK then
         if reused_session == false then
             return true