Handle payloads without XML declaration

[raintonr]

Some cameras post events as multipart messages without XML declaration. Eg (thanks to @BlackandGold1 for the example):

--boundary Content-Disposition: form-data; name="fielddetection" Content-Type: application/xml Content-Length: 1185 <EventNotificationAlert version="2.0" xmlns="http://www.hikvision.com/ver20/XMLSchema"> <ipAddress>10.11.12.100</ipAddress> <portNo>8089</portNo> <protocol>HTTP</protocol> <macAddress>80:7c:62:76:15:b8</macAddress> <channelID>1</channelID> <dateTime>2022-12-13T10:43:47+01:00</dateTime> <activePostCount>1</activePostCount> <eventType>fielddetection</eventType> <eventState>active</eventState> <eventDescription>fielddetection alarm</eventDescription> <DetectionRegionList> <DetectionRegionEntry> <regionID>3</regionID> <sensitivityLevel>50</sensitivityLevel> <RegionCoordinatesList> <RegionCoordinates> <positionX>671</positionX> <positionY>977</positionY> </RegionCoordinates> <RegionCoordinates> <positionX>489</positionX> <positionY>998</positionY> </RegionCoordinates> <RegionCoordinates> <positionX>485</positionX> <positionY>869</positionY> </RegionCoordinates> <RegionCoordinates> <positionX>690</positionX> <positionY>892</positionY> </RegionCoordinates> </RegionCoordinatesList> </DetectionRegionEntry> </DetectionRegionList> <channelName>IPdome</channelName> <isDataRetransmission>false</isDataRetransmission> </EventNotificationAlert> --boundary--

--boundary Content-Disposition: form-data; name="fielddetection" Content-Type: application/xml Content-Length: 1185 
<EventNotificationAlert version="2.0"
	xmlns="http://www.hikvision.com/ver20/XMLSchema">
	<ipAddress>10.11.12.100</ipAddress>
	<portNo>8089</portNo>
	<protocol>HTTP</protocol>
	<macAddress>80:7c:62:76:15:b8</macAddress>
	<channelID>1</channelID>
	<dateTime>2022-12-13T10:43:47+01:00</dateTime>
	<activePostCount>1</activePostCount>
	<eventType>fielddetection</eventType>
	<eventState>active</eventState>
	<eventDescription>fielddetection alarm</eventDescription>
	<DetectionRegionList>
		<DetectionRegionEntry>
			<regionID>3</regionID>
			<sensitivityLevel>50</sensitivityLevel>
			<RegionCoordinatesList>
				<RegionCoordinates>
					<positionX>671</positionX>
					<positionY>977</positionY>
				</RegionCoordinates>
				<RegionCoordinates>
					<positionX>489</positionX>
					<positionY>998</positionY>
				</RegionCoordinates>
				<RegionCoordinates>
					<positionX>485</positionX>
					<positionY>869</positionY>
				</RegionCoordinates>
				<RegionCoordinates>
					<positionX>690</positionX>
					<positionY>892</positionY>
				</RegionCoordinates>
			</RegionCoordinatesList>
		</DetectionRegionEntry>
	</DetectionRegionList>
	<channelName>IPdome</channelName>
	<isDataRetransmission>false</isDataRetransmission>
</EventNotificationAlert>
--boundary--