refineCentroids: Error: subscript out of bounds if the only centroid is on position 1

[Pascallio]

Hi, this issue may be related to issue #102 but since the results are different, I thought a separate issue might be more appropriate.

If I adapt the example code for the pidx to only have a centroid on position 1 an error occurs:

ints <- c(12, 8, 12, 7, 4, 9, 15, 16, 11, 8, 3, 2, 3, 9, 12, 14, 13, 8, 3)
mzs <- seq_along(ints)
pidx <- as.integer(1)

MsCoreUtils::refineCentroids(
    mzs, 
    ints, 
    pidx,
    k = 3L, 
    descending = TRUE, 
    threshold = .33
)

Gives:

Error in v[, "left"] : subscript out of bounds

This does not occur if the centroid is on any other position or if more than 1 centroid is defined.
It also does not throw an error if descending = FALSE.