Clean up error throwing code in UDP sockets

[Jarred-Sumner]

What does this PR do?

JSC.Maybe(void).errnoSys can return null if errno is 0. This leads to a null pointer dereference, most likely causing the below crash:

Bun v1.2.1 (ce53290) on linux x86_64 [AutoCommand]

Segmentation fault at address 0x00000000

uws.zig:4563: src.bun.js.api.bun.udp_socket.UDPSocket.setMembership
udp_socket.zig:469: UDPSocketPrototype__addMembership
ZigGeneratedClasses.cpp:47883: WebCore::UDPSocketPrototype__addMembershipCallback
1 unknown/js code
ld-temp.o:0: llint_op_call_ignore_result
ld-temp.o:0: llint_op_call_ignore_result
ld-temp.o:0: llint_op_call_ignore_result
ld-temp.o:0: llint_op_call_ignore_result

How did you verify your code works?

[robobun]

^{Updated 10:27 PM PT - Jan 31st, 2025}

❌ @Jarred-Sumner, your commit aebbe91 has some failures in Build #10961

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🧪   try this PR locally:

bunx bun-pr 16959