Tools panics when register-run directory doesn't exist

[wsodsong]

Tools panics when --register-run <folder> is used but, but the folder doesn't exists. An error should be thrown with a proper message.

stat /var/data/Aida/register-run-db: no such file or directory
sending forward recovered panic from PostRun; runtime error: invalid memory address or nil pointer dereference
goroutine 1 [running]:
runtime/debug.Stack()
	/home/wawa/go/pkg/mod/golang.org/[email protected]/src/runtime/debug/stack.go:24 +0x5e
github.com/Fantom-foundation/Aida/executor.signalPostRun[...].func1()
	/home/wawa/aida/executor/executor.go:574 +0x3d
panic({0x12c1200?, 0x2036db0?})
	/home/wawa/go/pkg/mod/golang.org/[email protected]/src/runtime/panic.go:770 +0x132
github.com/Fantom-foundation/Aida/executor/extension/register.(*registerProgress).PostRun(0xc007a9e820, {0xc0e05b9500?, 0x2?, {0x0?, 0x0?}}, 0xc0a59fdf80?, {0x16f15c0, 0xc0a59fdc08})
	/home/wawa/aida/executor/extension/register/register_progress.go:258 +0x19b
github.com/Fantom-foundation/Aida/executor.signalPostRun[...].func2()
	/home/wawa/aida/executor/executor.go:580 +0x42
github.com/Fantom-foundation/Aida/executor.forEachBackward[...]({0xc000002000?, 0x18, 0x767b8d02a8d8?}, 0xc0a425b118?)
	/home/wawa/aida/executor/executor.go:649 +0x8f
github.com/Fantom-foundation/Aida/executor.signalPostRun[...]({0x1?, 0xc007a9ff80?, {0x0?, 0x0?}}, 0xc0000511f0?, {0x16f15c0?, 0xc0a59fdc08?}, {0xc000002000, 0x17, 0x18})
	/home/wawa/aida/executor/executor.go:579 +0x114
github.com/Fantom-foundation/Aida/executor.(*executor[...]).Run.func1()
	/home/wawa/aida/executor/executor.go:262 +0xe7
github.com/Fantom-foundation/Aida/executor.(*executor[...]).Run(0x1716320, {0x45a43a, 0x54e67b, {0x0, 0x0}, 0x1, 0x1}, {0x16f15a0, 0xc00ed60068}, {0xc000002000, ...}, ...)
	/home/wawa/aida/executor/executor.go:268 +0x499
main.runSubstates(0xc00015d688, {0x16f57f0, 0xc0079b4100}, {0x0, 0x0}, {0x16f15a0, 0xc00ed60068}, {0x0, 0x0, 0x0}, ...)
	/home/wawa/aida/cmd/aida-vm-sdb/run_substate.go:107 +0xc76
main.RunSubstate(0xc000328000)
	/home/wawa/aida/cmd/aida-vm-sdb/run_substate.go:56 +0x25b
github.com/urfave/cli/v2.(*Command).Run(0x2060ac0, 0xc000328000, {0xc000483880, 0x1b, 0x1b})
	/home/wawa/go/pkg/mod/github.com/urfave/cli/[email protected]/command.go:276 +0x97d
github.com/urfave/cli/v2.(*Command).Run(0xc0001cedc0, 0xc0000ddec0, {0xc000188380, 0x1c, 0x1c})
	/home/wawa/go/pkg/mod/github.com/urfave/cli/[email protected]/command.go:269 +0xbb7
github.com/urfave/cli/v2.(*App).RunContext(0x2063d40, {0x16fcc48, 0x21373a0}, {0xc000188380, 0x1c, 0x1c})
	/home/wawa/go/pkg/mod/github.com/urfave/cli/[email protected]/app.go:333 +0x58b
github.com/urfave/cli/v2.(*App).Run(...)
	/home/wawa/go/pkg/mod/github.com/urfave/cli/[email protected]/app.go:307
main.main()
	/home/wawa/aida/cmd/aida-vm-sdb/main.go:181 +0x45