HACK around FB6940492: Mac Catalyst: Crash when presenting view controllers. Call early.

SomeObjCFile.m

/**
 HACK around FB6940492: Mac Catalyst: Crash when presenting view controllers

 'NSRangeException', reason: 'Cannot remove an observer <UINSSceneViewController 0x600003558790> for the key path "view.window.screen.contentLayoutRect" from <UINSSceneViewController 0x600003558790> because it is not registered as an observer.'

 0   CoreFoundation                      0x00007fff3b20f183 __exceptionPreprocess + 250
 1   libobjc.A.dylib                     0x00007fff71719b64 objc_exception_throw + 48
 2   Foundation                          0x00007fff3d8ca2aa -[NSObject(NSKeyValueObserverRegistration) _removeObserver:forProperty:] + 578
 3   Foundation                          0x00007fff3d8ca01b -[NSObject(NSKeyValueObserverRegistration) removeObserver:forKeyPath:] + 74
 4   Foundation                          0x00007fff3d8e2898 -[NSObject(NSKeyValueObserverRegistration) removeObserver:forKeyPath:context:] + 190
 5   UIKitMacHelper                      0x00007fff6c11e8ee -[UINSSceneViewController dealloc] + 298
 6   Foundation                          0x00007fff3d92f822 NSKVODeallocate + 172
 7   AppKit                              0x00007fff38518baa -[NSViewController release] + 119
 8   AppKit                              0x00007fff3869207e -[NSAutounbinder dealloc] + 44
 9   libobjc.A.dylib                     0x00007fff7172952a _ZN19AutoreleasePoolPage12releaseUntilEPP11objc_object + 134
 10  libobjc.A.dylib                     0x00007fff7170fc30 objc_autoreleasePoolPop + 175
 11  FrontBoardServices                  0x00007fff56e73255 -[FBSWorkspace _calloutQueue_executeCalloutFromSource:withBlock:] + 228
 12  FrontBoardServices                  0x00007fff56e8a4bf __84-[FBSWorkspaceScenesClient _queue_invalidateScene:withTransitionContext:completion:]_block_invoke + 290
 13  libdispatch.dylib                   0x000000010dd9f84f _dispatch_client_callout + 8
 14  libdispatch.dylib                   0x000000010dda30a3 _dispatch_block_invoke_direct + 289
 15  FrontBoardServices                  0x00007fff56e59508 __FBSSERIALQUEUE_IS_CALLING_OUT_TO_A_BLOCK__ + 30
 */
void PSPDFHackEatNSRangeExceptionsInSceneViewControllerDeallocation(void) {
    let clazz = NSClassFromString(@"UINSSceneViewController");
    if (!clazz) { return; }
    let selector = NSSelectorFromString(@"dealloc");
    __block IMP originalIMP = pspdf_swizzleSelectorWithBlock(clazz, selector, ^(__unsafe_unretained id _self) {
        @try {
            ((void (*)(id, SEL))originalIMP)(_self, selector);
        } @catch (...) {}
    });
}

Confused by my use of let? https://pspdfkit.com/blog/2017/even-swiftier-objective-c/#var-and-let