fix leaflet-compass on iPhoneOS

fixes stefanocudini/leaflet-compass#15
cf. domoritz/leaflet-locatecontrol#267

note: the request for permission may only be asked as response to
a user gesture (either click or touchend event), and via https;
not localhost/file

via: https://developer.apple.com/forums/thread/128376

https://stackoverflow.com/a/60239824/2171120 indicates that
exiting (swiping away) then restarting Safari will clear the
“asked?” status and this seems to wfm

LICENCE

@@ -1,6 +1,6 @@
 MirKarte itself is covered by The MirOS Licence:
 
-# Copyright © 2014, 2015, 2017, 2018, 2020
+# Copyright © 2014, 2015, 2017, 2018, 2020, 2022
 #	mirabilos <m@mirbsd.org>
 #
 # Provided that these terms and disclaimer and all copyright notices

leaflet-compass/leaflet-compass.js

@@ -146,15 +146,31 @@ L.Control.Compass = L.Control.extend({
 		return this._currentAngle;
 	},
 
-	activate: function() {
-
+	_activate: function () {
 		this._isActive = true;
 
 		L.DomEvent.on(window, 'deviceorientation', this._rotateHandler, this);
 
 		L.DomUtil.addClass(this._button, 'active');
 	},
 
+	activate: function () {
+		if (typeof(DeviceOrientationEvent) !== 'undefined' &&
+		    typeof(DeviceOrientationEvent.requestPermission) === 'function') {
+			/* iPhoneOS, must ask interactively */
+			var that = this;
+			DeviceOrientationEvent.requestPermission().then(function (permission) {
+				if (permission === 'granted')
+					that._activate();
+				else
+					alert('Cannot activate compass: permission ' + permission);
+			    }, function (reason) {
+				alert('Error activating compass: ' + reason);
+			    });
+		} else
+			this._activate();
+	},
+
 	deactivate: function() {
 
 		this.setAngle(0);