Input display seems to use hardcoded `0` instead of `AxisSpec.Neutral` when under specific circumstances

[YoshiRulz]

This is the previous frame value (grey text by default). Example use case is PSX, where Neutral is 128 for the analog sticks.

Works correctly (nothing is shown):

• Traditional recording (File > Movie > Record Movie... > OK)
• Load TAStudio project which was seeked(?) to frame ≥ 1 when it was saved

Shows zeroes:

• New TAStudio project (Tools > TAStudio, or via TAStudio's menubar)
• Load TAStudio project which was seeked(?) to frame 0 when it was saved
• Playback .bk2
• Playback .tasproj (w/o TAStudio)

In TAStudio, if you step forward and then back, it disappears, but clicking in the marker column does nothing (it must have a guard clause to skip seeking to the current frame).

see also #3685