[Submix][Recording] - Existing Sound Wave to Overwrite option has no effect

This is an old bug that looks like it never made its way into JIRA. Adding for documentation. 

1) Launch AudioQA
2) Navigate to Levels > Manual > AQ_SoundSubmixAssets > LevelAssets
3) Open UI_SubmixRecordingTest
4) Open the Blueprint graph
5) Locate the Stop Recording section. On the Finish Recording Output node set Export Type to Sound Wave
6) Press the Down arrow on the node to bring up the additional options
7) In Existing Sound Wave to Overwrite, select any Sound Wave asset
8) Open the level Levels > Manual > AQ_SoundSubmix
9) PIE
10) Navigate to the Recording UI Toggle
11) Move the pawn towards the button to start audio playing
12) Enter the Recording box
13) Press Start, wait a bit, then press Stop to finish recording the audio
14) Stop PIE
15) Locate the Sound Wave you chose to overwrite. Play the sound

Expected Result:
 The Sound Wave is overwritten with the recorded audio

Actual Result:
 The Sound Wave is not overwritten. Instead, a new Sound Wave is created and added to the Content folder