HashMap: Tolerate reserving for 0 elements
HashMap: Tolerate reserving for 0 elements

Fixes #1652

casimir/kakoune,jkonecny12/kakoune,mawww/kakoune,occivink/kakoune,alexherbo2/kakoune,jkonecny12/kakoune,alexherbo2/kakoune,alexherbo2/kakoune,jjthrash/kakoune,jkonecny12/kakoune,mawww/kakoune,Somasis/kakoune,jkonecny12/kakoune,lenormf/kakoune,casimir/kakoune,occivink/kakoune,lenormf/kakoune,Somasis/kakoune,mawww/kakoune,alexherbo2/kakoune,danr/kakoune,jjthrash/kakoune,danr/kakoune,jjthrash/kakoune,casimir/kakoune,occivink/kakoune,danr/kakoune,Somasis/kakoune,occivink/kakoune,mawww/kakoune,danr/kakoune,casimir/kakoune,lenormf/kakoune,Somasis/kakoune,lenormf/kakoune,jjthrash/kakoune