consensusString and consensusMatrix error for legth-0 input

[jan-glx]

Currently, consensusString fails for length-0 inputs:

Biostrings::consensusString(character(0))
#> Error in h(simpleError(msg, call)): error in evaluating the argument 'x' in selecting a method for function 'consensusString': 'x' has no element and 'width' is NULL

^{Created on 2023-07-29 by the reprex package (v2.0.1)}

I believe it should return character(0) instead and at most warn.

Maybe, replacing error("'x' has no element and 'width' is NULL"); with return allocMatrix(INTSXP, 0, 0); is all that's needed?