mail: reset the content buffer before each part

When io.Copy from a part body failed, the loop continued without
clearing the shared buffer, so leftover bytes from the failed part were
carried into the next text part. Reset the buffer at the start of every
iteration so each part starts clean.

Signed-off-by: Robin Jarry <robin@jarry.cc>

Author: rjarry

pkg/mail/content.go

@@ -55,6 +55,7 @@ func findTextParts(m *mail.Reader) []textPart {
 			continue
 		}
 
+		buf.Reset()
 		if n, err := io.Copy(&buf, part.Body); err != nil {
 			log.Warnf("failed to read part body: %s", err)
 			continue
@@ -66,8 +67,6 @@ func findTextParts(m *mail.Reader) []textPart {
 			payload: strings.ReplaceAll(buf.String(), "\r\n", "\n"),
 			subtype: subtype,
 		})
-
-		buf.Reset()
 	}
 
 	return results