OSX: First responder warning

[FredrikNoren]

Hi, I'm getting the following warning sometimes (it doesn't seem like every time) when running this wry/tao on OSX:

[General] ERROR: Setting <TaoView: 0x1097505b0> as the first responder for window <TaoWindow: 0x109745850>, but it is in a different window ((null))! This would eventually crash when the view is freed. The first responder will be set to nil.
(
0 AppKit 0x000000018da7ceb8 -[NSWindow _validateFirstResponder:] + 436
1 AppKit 0x000000018da7cca0 -[NSWindow _setFirstResponder:] + 36
2 AppKit 0x000000018db90728 -[NSWindow _realMakeFirstResponder:] + 400
3 dims 0x00000001027fb7c0 _ZN14objc_exception10try_no_ret24try_objc_execute_closure17h6d70081023a997c7E + 56
4 dims 0x0000000102a53f64 RustObjCExceptionTryCatch + 28
5 dims 0x00000001027fd964 _ZN4objc7message8platform15send_unverified17h872d681f7da63a39E + 100
6 dims 0x00000001027f9b04 ZN77$LT$$BP$mut$u20$objc..runtime..Object$u20$as$u20$cocoa..appkit..NSWindow$GT$19makeFirstResponder_17h9c3093a44cd97cafE + 76
7 dims 0x0000000100c55124 _ZN8dispatch20context_and_function20work_execute_closure17h652d613b660c00ccE + 108
8 libdispatch.dylib 0x000000018ac8abac _dispatch_client_callout + 20
9 libdispatch.dylib 0x000000018ac990ac _dispatch_main_queue_callback_4CF + 944
10 CoreFoundation 0x000000018af55e60 CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE + 16
11 CoreFoundation 0x000000018af13820 __CFRunLoopRun + 2540
12 CoreFoundation 0x000000018af12694 CFRunLoopRunSpecific + 600
13 HIToolbox 0x0000000193a88990 RunCurrentEventLoopInMode + 292
14 HIToolbox 0x0000000193a88704 ReceiveNextEventCommon + 552
15 HIToolbox 0x0000000193a884c4 _BlockUntilNextEventMatchingListInModeWithFilter + 72
16 AppKit 0x000000018da67aec _DPSNextEvent + 844
17 AppKit 0x000000018da66390 -[NSApplication(NSEvent) _nextEventMatchingEventMask:untilDate:inMode:dequeue:] + 1332
18 AppKit 0x000000018da583b0 -[NSApplication run] + 596
19 dims 0x0000000100bd4984 _ZN14objc_exception10try_no_ret24try_objc_execute_closure17h2c822b8f96de4baeE + 48
20 dims 0x0000000102a53f64 RustObjCExceptionTryCatch + 28
21 dims 0x0000000100be3254 _ZN4objc7message8platform15send_unverified17he7912b788ff81a35E + 92
22 dims 0x0000000100b976f8 _ZN3tao13platform_impl8platform10event_loop18EventLoop$LT$T$GT$3run17hab28f06791f675ebE + 560
23 dims 0x0000000100c013f4 _ZN3tao13platform_impl8platform9app_state8AppState12set_callback17h171eb45c9fe5bcf2E + 0
24 dims 0x0000000100c0d03c _ZN18dims_asset_browser6window18main_asset_browser17h3b000ea9b08805bbE + 2016
25 dims 0x0000000100119660 _ZN4dims4main17h3376322af5eb8f6fE + 2460
26 dims 0x0000000100124018 _ZN3std10sys_common9backtrace28__rust_begin_short_backtrace17h28d2c4fbdc240934E + 12
27 dims 0x000000010006113c ZN3std2rt10lang_start28$u7b$$u7b$closure$u7d$$u7d$17hfc5ff969bed65504E + 16
28 dims 0x0000000102ddfcdc _ZN3std2rt19lang_start_internal17h9a76c1e984d480efE + 540
29 dims 0x000000010011a39c main + 48
30 dyld 0x0000000108e890f4 start + 520

Guess it could be related to #208