Sequencer XML generates wrong File Path for Image Sequence

Outputing Image Sequences like

{shot}/{shot}

_

{frame}

.png for example, the xml file doesn't reflect the right path because it's referring to .avi files. We can't find and replace avi files in the xml files because sequences files have to be output in there own folder.

This issue was reported and tested in 4.20.2 (CL-4302132). This was reproduced in Main 4.21 (CL-4347190). This wasn't present in 4.19.2 (CL-4033788) as the XML file wasn't generated.

1. Open the UE4 Editor and create a Blank Template project
2. Click on Cinematics > Add a Master Sequence > Create Master Sequence
3. Click the button to render the Master Sequence to a video or image sequence
4. Change the Output Format to any Image Sequence
5. Click Capture Movie, stop the movie capture after a few seconds, then open the capture folder
6. Open the .xml file

Results:The XML refers to .avi movie files even if we output images sequences

Expected: Xml files refers to the right output file path.