[Bug] Not working with non-square maze

[anhgelus]

When we create a maze with -w != -h, there is two possibility:

If -w > -h

Throw an error like this:

panic: the wall with the id X have only 4 cells near

goroutine 1 [running]:
main.main()
        maze-generator-cli/main.go:44 +0x413
exit status 2

If -w < -h

panic: runtime error: index out of range [27] with length 25

goroutine 1 [running]:
github.com/msmp-core/maze-generator-cli/Generators.(*Maze).generateCells(0xc00006def0)
        maze-generator-cli/Generators/global.go:79 +0x65a
github.com/msmp-core/maze-generator-cli/Generators.NewRandomisedKruskal(0xc00001e159?)
        maze-generator-cli/Generators/randomised_kruskal.go:17 +0x17b
github.com/msmp-core/maze-generator-cli/Generators.GenerateNewMaze(...)
        maze-generator-cli/Generators/global.go:43
main.main()
        maze-generator-cli/main.go:42 +0x3a6
exit status 2