Hovering over an image for alt text causes `NSException` on macOS 12.1 w/ M1

[jkelleyrtp]

I think there's a bug in Webkit 15, but I'm reporting it here anyways since I haven't had a chance to try a go/c++ app.

If you hover over an image in the minimal example, web-view crashes with the following error:

2021-12-26 21:06:06.567 minimal[49120:617997] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[__NSPlaceholderDictionary initWithObjects:forKeys:count:]: attempt to insert nil object from objects[15]'
*** First throw call stack:
(
        0   CoreFoundation                      0x000000018e0c81cc __exceptionPreprocess + 240
        1   libobjc.A.dylib                     0x000000018de197b8 objc_exception_throw + 60
        2   CoreFoundation                      0x000000018e198488 -[__NSCFString characterAtIndex:].cold.1 + 0
        3   CoreFoundation                      0x000000018e1a50c4 -[__NSPlaceholderDictionary initWithCapacity:].cold.1 + 0
        4   CoreFoundation                      0x000000018dfcfed0 -[__NSPlaceholderDictionary initWithObjects:forKeys:count:] + 320
        5   CoreFoundation                      0x000000018dfcfd64 +[NSDictionary dictionaryWithObjects:forKeys:count:] + 60
        6   VisionKitCore                       0x0000000204ca7e08 -[VKAnalyticsAnalyzerEvent coreAnalyticsDictionary] + 1208
        7   VisionKitCore                       0x0000000204c6ab00 -[VKAnalyticsProcessor processAndSendEvent:] + 92
        8   VisionKitCore                       0x0000000204c607d8 __69-[VKImageAnalyzer _processRequest:progressHandler:completionHandler:]_block_invoke_2 + 1200
        9   libdispatch.dylib                   0x000000018ddbce60 _dispatch_call_block_and_release + 32
        10  libdispatch.dylib                   0x000000018ddbebac _dispatch_client_callout + 20
        11  libdispatch.dylib                   0x000000018ddc6330 _dispatch_lane_serial_drain + 672
        12  libdispatch.dylib                   0x000000018ddc6ea4 _dispatch_lane_invoke + 392
        13  libdispatch.dylib                   0x000000018ddd1708 _dispatch_workloop_worker_thread + 656
        14  libsystem_pthread.dylib             0x000000018df79304 _pthread_wqthread + 288
        15  libsystem_pthread.dylib             0x000000018df78018 start_wqthread + 8
)
libc++abi: terminating with uncaught exception of type NSException
[1]    49120 abort      cargo run --example minimal