MeanDims fails when averaging all the dimensions

Hi @nperez, @aho,

I have found a little bug in MeanDims() function when trying to average all the dimensions of an array (it works perfect for the rest of the cases). This is an example:

> x <- array(1:40, dim = list(a = 2, b = 4, c = 6))
> MeanDims(data = x, dims = c('a','b','c'))
Error in dim(newX) <- c(prod(d.call), d2) : 
  dims [product 1] do not match the length of object [48]

A possible fix would be to change lines 81-84 for the following ones:

if (length(margins) == 0){
  res <- mean(data, na.rm = na.rm)
} else {
  res <- as.array(apply(data, margins, mean, na.rm = na.rm))
  if (!is.null(names(dim(data))[margins]) & is.null(names(dim(res)))) {
    names(dim(res)) <- names(dim(data))[margins]
  }
}

Best regards,

Carlos