uhttpd: HTTP request smuggling via ubus POST body parse-error desync

uhttpd is a small HTTP server. In unpatched repository snapshots, uh_ubus_data_send() in ubus.c can desynchronize HTTP request boundaries when a POST /ubus JSON body arrives in multiple TCP segments. An initial segment completing a JSON object sets du->jsobj; a later segment takes the existing-object parse-error path and returns zero bytes consumed. The caller neither drains the remaining declared Content-Length nor sets connection_close. An HTTP request embedded in the unread body suffix is consequently processed as a new request on the same keep-alive connection. The reported reproducer returned a JSON-RPC parse error followed by a second HTTP response. This application-layer body-handler flaw is distinct from Transfer-Encoding header case handling and chunk-length state reset, and affects deployments enabling ubus, including the default OpenWrt configuration and potential proxy/CDN deployments. Repository patches 7b1bec45826bd78c8afc993435bdc0f1df2fe399 and b2285de129b9adc8b12f84f9a27c16c21f2b57a5 address this issue.