separate_arguments: Fix crash on UNIX_COMMAND with no arguments
I made this change as a by product of trying to compile another open-source-project "neovim" which would not compile. Neovim uses CMake and following the build instructions the build was failing with a "Segmentation Fault".
Fixes: #21320 (closed)
Backport: release
Topic-rename: separate_arguments-no-args
Edited by Brad King