Pattern for action decision

I am writing maze generator and at the some point I have to choose random unvisited neighbour of a cell. The first idea was just to enumerate neighbours such as left = 0, top = 1, right = 2, bottom = 3 and use rand() % 4 to generate random number and choose appropriate cell. However, not all cells features 4 neighbours, so that I had to write following code:

Cell* getRandomNeighbour(const Maze* const maze, const Cell* const currentCell) {

int randomNumb = rand() % 4;

int timer = 1;

while(timer > 0) {
    if (randomNumb == 0 && currentCell->x < maze->width-1 && maze->map[currentCell->y][currentCell->x+1].isUnvisited) 
        return &maze->map[currentCell->y][currentCell->x+1];
    if (randomNumb == 1 && currentCell->x > 0 && maze->map[currentCell->y][currentCell->x-1].isUnvisited) 
        return &maze->map[currentCell->y][currentCell->x-1];
    if (randomNumb == 2 && currentCell->y < maze->height-1 && maze->map[currentCell->y+1][currentCell->x].isUnvisited) 
        return &maze->map[currentCell->y+1][currentCell->x];
    if (randomNumb == 3 && currentCell->y > 0 && maze->map[currentCell->y-1][currentCell->x].isUnvisited) 
        return &maze->map[currentCell->y-1][currentCell->x];

    timer--;
    randomNumb = rand() % 4;
}


if (currentCell->x < maze->width-1 && maze->map[currentCell->y][currentCell->x+1].isUnvisited) 
    return &maze->map[currentCell->y][currentCell->x+1];
if (currentCell->x > 0 && maze->map[currentCell->y][currentCell->x-1].isUnvisited) 
    return &maze->map[currentCell->y][currentCell->x-1];
if (currentCell->y < maze->height-1 && maze->map[currentCell->y+1][currentCell->x].isUnvisited) 
    return &maze->map[currentCell->y+1][currentCell->x];
if (currentCell->y > 0 && maze->map[currentCell->y-1][currentCell->x].isUnvisited) 
    return &maze->map[currentCell->y-1][currentCell->x];

return NULL;
}

So, if after 10 iterations the right decision isn't chosen, it will be picked by brute force. This approach seems to be good for the reason that varying of variable timer changes the complexity of maze: the less timer is, the more straightforward maze is. Nevertheless, if my only purpose is to generate completely random maze, it takes a lot of execution time and look a little bit ugly. Is there any pattern(in C language) or way of refactoring that could enable me to deal with this situation without long switches and a lot of if-else constructions?