Avoid matrix allocation when size is zero.
Avoid matrix allocation when size is zero.

NicolasSchnitzler/dtk,NicolasSchnitzler/dtk,NicolasSchnitzler/dtk,d-tk/dtk,rdebroiz/dtk,rdebroiz/dtk,d-tk/dtk,rdebroiz/dtk,rdebroiz/dtk,d-tk/dtk,d-tk/dtk,d-tk/dtk,NicolasSchnitzler/dtk,d-tk/dtk