TransparentPointer fail

Dieses Issue hat noch niemand übernommen.

I'm trying to switch from using the [flutter-mapbox-gl](https://github.com/flutter-mapbox-gl/maps) plugin to this one, and I ran into an issue...

I'm using a [transparent pointer](https://pub.dev/packages/transparent_pointer) over the map, in a Stack widget, so I can turn off some automated panning and zooming if the user starts interacting with the map; I'm interpreting gestures as pans, zooms, and rotates, and also letting the gestures bubble through to the map. This works fine with that other mapbox plugin, but with this one I get:

```
I/flutter ( 8823): ⚠️ Unhandled Flutter error: 'package:flutter/src/gestures/tap.dart': Failed assertion: line 210 pos 14: '_down == null && _up == null': is not true.

======== Exception caught by gesture library =======================================================
The following assertion was thrown while dispatching a pointer event:
'package:flutter/src/gestures/tap.dart': Failed assertion: line 210 pos 14: '_down == null && _up == null': is not true.

Either the assertion indicates an error in the framework itself, or we should provide substantially more information in this error message to help you determine and fix the underlying cause.
In either case, please report this assertion by filing a bug on GitHub:
https://github.com/flutter/flutter/issues/new?template=2_bug.md

When the exception was thrown, this was the stack:
#2 BaseTapGestureRecognizer.addAllowedPointer (package:flutter/src/gestures/tap.dart:210:14)
#3 GestureRecognizer.addPointer (package:flutter/src/gestures/recognizer.dart:160:7)
#4 RawGestureDetectorState._handlePointerDown (package:flutter/src/widgets/gesture_detector.dart:1498:18)
#5 RenderPointerListener.handleEvent (package:flutter/src/rendering/proxy_box.dart:3168:29)
#6 GestureBinding.dispatchEvent (package:flutter/src/gestures/binding.dart:440:22)
#7 RendererBinding.dispatchEvent (package:flutter/src/rendering/binding.dart:336:11)
#8 GestureBinding._handlePointerEventImmediately (package:flutter/src/gestures/binding.dart:395:7)
#9 GestureBinding.handlePointerEvent (package:flutter/src/gestures/binding.dart:357:5)
#10 GestureBinding._flushPointerEventQueue (package:flutter/src/gestures/binding.dart:314:7)
#11 GestureBinding._handlePointerDataPacket (package:flutter/src/gestures/binding.dart:295:7)
#12 _invoke1 (dart:ui/hooks.dart:164:13)
#13 PlatformDispatcher._dispatchPointerDataPacket (dart:ui/platform_dispatcher.dart:361:7)
#14 _dispatchPointerDataPacket (dart:ui/hooks.dart:91:31)
(elided 2 frames from class _AssertionError)
Event: PointerDownEvent#85236(position: Offset(222.0, 753.2))
position: Offset(222.0, 753.2)
Target: RenderPointerListener#00676 relayoutBoundary=up8
parentData: (can use size)
constraints: BoxConstraints(0.0<=w<=411.4, 0.0<=h<=819.4)
size: Size(411.4, 819.4)
behavior: deferToChild
listeners: down, panZoomStart
```

Is there a way to make this work?

Alternatively, is there a way to listen for *user initiated* zooms, pans, and rotates with this package?

Beginne damit, die Assertion mit transparent_pointer über der Map in einem Stack zu reproduzieren, unter Verwendung der im Report gezeigten Gesture-Callbacks. Lies den Flutter-Gesture-Stack rund um tap.dart, gesture_detector.dart und die Gesture-Einstiegspunkte des Map-Pakets; abgeschlossen ist die Aufgabe, wenn die Interaktion keine Assertion mehr auslöst und vom Benutzer initiierte Pan-, Zoom- und Rotate-Gesten unterschieden oder dokumentiert werden können.

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