Better json_decode exception handling

[Pilskalns]

Wrap json_decode in proper handling for strict syntax checks.

Fixes #882

[wintrue]

There are still mistakes.

[wintrue]

string(102) "{"id":"20231201095056.bb2a8c9f645a8ef7@xxx.com.hk","message":"Queued. Thank you."}
"
^ Mailgun\Exception\HydrationException {#122
#message: "Error (4) when trying to json_decode response"
#code: 0
#file: "/var/www/server/shawprize/server/vendor/mailgun/mailgun-php/src/Hydrator/ModelHydrator.php"
#line: 42
trace: {
/var/www/server/shawprize/server/vendor/mailgun/mailgun-php/src/Hydrator/ModelHydrator.php:42 {}
/var/www/server/shawprize/server/vendor/mailgun/mailgun-php/src/Api/HttpApi.php:79 {}
/var/www/server/shawprize/server/vendor/mailgun/mailgun-php/src/Api/Message.php:77 {}
/var/www/server/shawprize/server/app/common/service/ExtHelperService.php:131 {
app\common\service\ExtHelperService::sendMail($address, $subject, $body) …
› # Make the call to the client.
› $result= $mgClient->messages()->send($domain, $params);
›