curl: libcurl MQTT `CURLOPT_POSTFIELDSIZE_LARGE` overflow leads to immediate DoS

Summary An attacker can crash or forcefully abort any application that uses libcurl's MQTT support by setting an excessively large value for CURLOPTPOSTFIELDSIZELARGE. The MQTT publish logic lib/mqtt.c::mqttpublish trusts this value without validating it against the protocol's maximum remaining...