Fix app crash when there is repeated SLEEP at the end of the "lines" slice

[alaingilbert]

I found the issue while testing a low value of 5ms for sleepThreshold

The goal was to create the same delays as what I actually type.

Here is some related comments ->
https://news.ycombinator.com/item?id=39298134

Here is the stacktrace you would get without the fix:

panic: runtime error: index out of range [634] with length 634

goroutine 1 [running]:
main.inputToTape({0xc0004d8000?, 0xc00014c000?})
	/Users/username/Documents/vhs/record.go:153 +0x15d8
main.Record(0xc000118700?, {0x285e9e0?, 0x4?, 0x1c2156c?})
	/Users/username/Documents/vhs/record.go:117 +0x613
github.com/spf13/cobra.(*Command).execute(0x280c140, {0x285e9e0, 0x0, 0x0})
	/Users/username/go/pkg/mod/github.com/spf13/[email protected]/command.go:983 +0xabc
github.com/spf13/cobra.(*Command).ExecuteC(0x280ccc0)
	/Users/username/go/pkg/mod/github.com/spf13/[email protected]/command.go:1115 +0x3ff
github.com/spf13/cobra.(*Command).Execute(...)
	/Users/username/go/pkg/mod/github.com/spf13/[email protected]/command.go:1039
github.com/spf13/cobra.(*Command).ExecuteContext(...)
	/Users/username/go/pkg/mod/github.com/spf13/[email protected]/command.go:1032
main.main()
	/Users/username/Documents/vhs/main.go:250 +0xc9
exit status 2

[maaslalani]

Thank you so much!

[maaslalani]

Awesome work again @alaingilbert, thank you!