Occasional crash in speech_to_text

[sowens-csd]

An application was crashing with a sigabrt in speech_to_text occasionally. Sometimes when coming back into the foreground, sometimes while running. The stack trace pointed to the invokeFlutter method in speech_to_text. Looks like the parameters were incorrect in the case of a speechRecognizer availabilityDidChange callback.

#0 (null) in __exceptionPreprocess ()
#1 (null) in objc_exception_throw ()
#2 (null) in +[NSException raise:format:arguments:] ()
#3 (null) in -[NSAssertionHandler handleFailureInMethod:object:file:lineNumber:description:] ()
#4 (null) in -[FlutterStandardWriter writeValue:] ()
#5 0x37553a in -[FlutterStandardMethodCodec encodeMethodCall:] ()
#6 0x3723f2 in -[FlutterMethodChannel invokeMethod:arguments:] ()
#7 0xc07ae6 in partial apply for closure #1 in SwiftSpeechToTextPlugin.invokeFlutter(_:arguments:) at /Users/.../speech_to_text/ios/Classes/SwiftSpeechToTextPlugin.swift:262
#8 (null) in thunk for @escaping @callee_guaranteed () -> () ()
#9 (null) in _dispatch_call_block_and_release ()
#10 (null) in _dispatch_client_callout ()
#11 (null) in _dispatch_main_queue_callback_4CF ()
#12 (null) in CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE ()
#13 (null) in __CFRunLoopRun ()
#14 (null) in CFRunLoopRunSpecific ()
#15 (null) in CFRunLoopRunInMode ()
#16 (null) in GSEventRunModal ()
#17 (null) in UIApplicationMain ()