Unwrapping undefined optional is not safety-checked in safe modes

[mnemnion]

Zig Version

v0.14.0-dev.2238+1db8cade5

Steps to Reproduce and Observed Behavior

This passes in Debug mode, but fails in ReleaseFast:

test "unwrapped undefined optional" {
    var opt_block: ?[4096]u8 = undefined;
    opt_block.?[0] = '!';
    try expectEqual('!', opt_block.?[0]);
    try expect(opt_block != null);
    opt_block = null;
    try expect(opt_block == null);
}

Expected Behavior

Expect a panic when the some field is 0xaa on unwrap. The condition is detectable, because using @as([4096]u8, undefined) sets some to 0x01.

[nektro]

related #63
related #211

[mnemnion]

And the master issue #2301.

Maybe worth keeping this open as a specific case, because a fix for optionals which use the some + data structure is comparatively straightforward: unwrapping is already null-checked in safe modes, this could check specifically for 0x01 and handle both types of error on the cold path, which should be broadly as efficient when the program is not immediately on the verge of crashing.

Not as straightforward for pointers, no idea how any later niche optimizations would interact with Debug and ReleaseSafe, but that's a problem for later.