fix: update Slack file upload context and correct file size handling

Author: isaric

README.md

@@ -1,6 +1,6 @@
 # Onvif-Cam-Poll
 
-[![Go](https://github.com/isaric/onvif-cam-poll/actions/workflows/go.yml/badge.svg?branch=master)](https://github.com/isaric/onvif-cam-poll/actions/workflows/go.yml)
+[![Go](https://github.com/isaric/onvif-cam-poll/actions/workflows/go.yml/badge.svg?branch=main)](https://github.com/isaric/onvif-cam-poll/actions/workflows/go.yml)
 
 Four golang scripts that provide ONVIF motion event polling and time/date setting. The scripts were created to allow 
 the use of IP cameras without using a cloud service as a middle man between the user and the camera(s).

cmd/onvif-motion-poll/main.go

@@ -94,9 +94,9 @@ func getAndUploadSnapshot(url, channelID string, slackClient slack.Client) {
 		return
 	}
 
-	_, err := slackClient.UploadFileV2Context(slack.UploadFileV2Parameters{
+	_, err := slackClient.UploadFileV2Context(context.Background(), slack.UploadFileV2Parameters{
 		Reader:   r.Body,
-		FileSize: r.ContentLength,
+		FileSize: int(r.ContentLength),
 		Filename: fmt.Sprintf("%s.png", time.Now().Format("20060102150405")),
 		Channel: channelID,
 	})