modulecmd: return overlay root as prefix if not set

Pmodules/modulecmd.bash.in

@@ -1306,9 +1306,15 @@ get_overlay_info(){
 	for config_file in "${config_files[@]}"; do
 		[[ -r "${config_file}" ]] || continue
 		local toks=()
+		local -i lino=0
 		while read -a toks; do
+			(( lino++ ))
 			[[ -n "${toks[0]}" ]] || continue
 			[[ ${toks[0]} == \#* ]] && continue
+			(( ${#toks[@]} < 2 )) && \
+				std::warn "%s - %s" \
+					  "Skipping malformed line ${lino} in configuration file" \
+					  "${config_file}"
 			local _name="${toks[0]%:*}"
 			if [[ "${toks[0]%:*}" == "${name_or_dir}" ]] \
 				   || [[ "${toks[1]}" == "${name_or_dir}" ]]; then
@@ -1324,7 +1330,11 @@ get_overlay_info(){
 				fi
 				[[ -n "$2" ]] && std::upvar "$2" "${_type}"
 				[[ -n "$3" ]] && std::upvar "$3" "${toks[1]}"
-				[[ -n "$4" ]] && std::upvar "$4" "${toks[2]}"
+				if [[ -n "$4" ]]; then
+					std::upvar "$4" "${toks[2]}"
+				else
+					std::upvar "$4" "${toks[1]}"
+				fi
 				return 0
 			fi
 		done < "${config_file}"