Running with --interval and an invalid duration leads to nil pointer dereference

[AlexanderThaller]

» ./viddy --version
viddy version: 0.3.6

» ./viddy -n asdasd
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x40 pc=0x7df725]

goroutine 1 [running]:
main.main()
	/home/runner/work/viddy/viddy/main.go:43 +0x1c5