RCTTouchHandler assertion crash when rapidly tapping UIExplorer with multiple fingers

[ide]

Repro: Launch UIExplorer and rapidly tap on the screen repeatedly with four fingers. It seems to happen after one of the touches initiates a navigation and a lot more touches come in.

This is on the latest commit c88a1cd with iOS 8.2 and Xcode 6.2.

Exception Type:  EXC_CRASH (SIGABRT)
Exception Codes: 0x0000000000000000, 0x0000000000000000
Triggered by Thread:  0

Last Exception Backtrace:
0   CoreFoundation                  0x185556530 __exceptionPreprocess + 132
1   libobjc.A.dylib                 0x1964ec0e4 objc_exception_throw + 60
2   CoreFoundation                  0x1855563f0 +[NSException raise:format:arguments:] + 116
3   Foundation                      0x186401c34 -[NSAssertionHandler handleFailureInMethod:object:file:lineNumber:description:] + 112
4   UIExplorer                      0x10008a780 -[RCTTouchHandler _updateAndDispatchTouches:eventName:] (RCTTouchHandler.m:157)
5   UIExplorer                      0x10008aff0 -[RCTTouchHandler touchesCancelled:withEvent:] (RCTTouchHandler.m:206)
6   UIKit                           0x189d91b10 -[UIWindow _sendGesturesForEvent:] + 748
7   UIKit                           0x189d912d8 -[UIWindow sendEvent:] + 660
8   UIKit                           0x189d64be0 -[UIApplication sendEvent:] + 264
9   UIKit                           0x18a003f84 _UIApplicationHandleEventFromQueueEvent + 14992
10  UIKit                           0x189d63150 _UIApplicationHandleEventQueue + 1716
11  CoreFoundation                  0x18550ed34 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 24
12  CoreFoundation                  0x18550dfd8 __CFRunLoopDoSources0 + 264
13  CoreFoundation                  0x18550c088 __CFRunLoopRun + 712
14  CoreFoundation                  0x1854391f4 CFRunLoopRunSpecific + 396
15  GraphicsServices                0x18e8476fc GSEventRunModal + 168
16  UIKit                           0x189dc9e6c UIApplicationMain + 1488
17  UIExplorer                      0x10004bb04 main (main.m:8)
18  libdyld.dylib                   0x196b6aa08 start + 4

[tadeuzagallo]

Fixed on 258c6b1