Add /sbin to AppImage search path

Closes #4846

Author: tresf

cmake/linux/package_linux.sh.in

@@ -97,6 +97,7 @@ mv "${APPDIR}usr/bin/lmms" "${APPDIR}usr/bin/lmms.real"
 cat >"${APPDIR}usr/bin/lmms" <<EOL
 #!/usr/bin/env bash
 DIR="\$( cd "\$( dirname "\${BASH_SOURCE[0]}" )" && pwd )"
+export PATH="$PATH:/sbin"
 if which carla > /dev/null 2>&1; then
    CARLAPATH="\$(which carla)"
    CARLAPREFIX="\${CARLAPATH%/bin*}"