Fix error message for find_program if program cannot be found
Fix error message for find_program if program cannot be found

Currently this raises an exception because exename is undefined.

QuLogic/meson,QuLogic/meson,jpakkane/meson,ernestask/meson,mesonbuild/meson,ernestask/meson,ernestask/meson,jpakkane/meson,trhd/meson,QuLogic/meson,MathieuDuponchelle/meson,becm/meson,jpakkane/meson,jpakkane/meson,mesonbuild/meson,becm/meson,MathieuDuponchelle/meson,QuLogic/meson,trhd/meson,ernestask/meson,jeandet/meson,mesonbuild/meson,trhd/meson,pexip/meson,MathieuDuponchelle/meson,thiblahute/meson,pexip/meson,thiblahute/meson,QuLogic/meson,becm/meson,mesonbuild/meson,pexip/meson,QuLogic/meson,ernestask/meson,MathieuDuponchelle/meson,trhd/meson,pexip/meson,becm/meson,becm/meson,QuLogic/meson,ernestask/meson,ernestask/meson,mesonbuild/meson,jeandet/meson,thiblahute/meson,thiblahute/meson,ernestask/meson,jeandet/meson,trhd/meson,becm/meson,MathieuDuponchelle/meson,MathieuDuponchelle/meson,mesonbuild/meson,pexip/meson,pexip/meson,jeandet/meson,QuLogic/meson,trhd/meson,MathieuDuponchelle/meson,jpakkane/meson,becm/meson,becm/meson,thiblahute/meson,jpakkane/meson,pexip/meson,ernestask/meson,mesonbuild/meson,trhd/meson,thiblahute/meson,pexip/meson,jeandet/meson,jeandet/meson,jeandet/meson,pexip/meson,jeandet/meson,thiblahute/meson,jpakkane/meson,jeandet/meson,trhd/meson,pexip/meson,MathieuDuponchelle/meson,jpakkane/meson,mesonbuild/meson,mesonbuild/meson,mesonbuild/meson,trhd/meson,thiblahute/meson,jpakkane/meson,becm/meson,thiblahute/meson,becm/meson,MathieuDuponchelle/meson,QuLogic/meson