curl: CVE-2026-11352: QUIC zero-length UDP datagrams busy-loop

Summary: curl's QUIC UDP receive helper ignores zero-length UDP datagrams before counting them against the per-call packet budget. On Linux, recvmmsgpackets loops while pkts maxpkts, but if!mmsgi.msglen continue; runs before pkts is incremented. The recvmsgpackets backend has the same no-progress...