Tracks with different GAPs not displayed correctly in overview

[SarutaSan72]

Bug affects only display in track overview. The main editor area is correct.
--> Postponed to milestone 2.5.0

Example data:

file 1:

#TITLE: Lyrics Gap 1000ms and 300bpm (Track 1)
#ARTIST:Duet Test
#MP3:Test - Test.mp3
#BPM:300
#GAP:1000
: 3 3 0 3-3-0
: 8 3 0 8-3-0
- 12
: 13 3 0 13-3-0
: 18 3 0 18-3-0
E

file 2:

#TITLE: Lyrics Gap 1000ms and 300bpm (Track 2)
#ARTIST:Duet Test
#MP3:Test - Test.mp3
#BPM:300
#GAP:1000
: 13 3 0 13-3-0
: 18 3 0 18-3-0
E

file 3:

#TITLE: Lyrics Gap 1650ms and 300bpm (Track 3)
#ARTIST:Duet Test
#MP3:Test - Test.mp3
#BPM:300
#GAP:1650
: 0 3 0 0-3-0
: 5 3 0 5-3-0
E

File 3 is not displayed correctly in overview.

[SarutaSan72]

postponed; is this a real usecase?
first verify that duet features are commonly used