Merge branch '360-modulecmd-overlayexcludes-matches-everything-if-empty' into 'master'

Resolve "modulecmd: OverlayExcludes matches everything if empty"

Closes #360

See merge request Pmodules/src!367

(cherry picked from commit 99a168996f)

a86a0a7c modulecmd: bugfix in handling overlay excludes

Co-authored-by: gsell <achim.gsell@psi.ch>

Pmodules/modulecmd.bash.in

@@ -1217,7 +1217,7 @@ get_available_modules() {
 		# its sub-directories
 		local mod=''	# module_name/module_version
                 while read -r mod; do
-			[[ "${mod}" =~ ${OverlayExcludes} ]] && continue
+			[[ -n ${OverlayExcludes} && "${mod}" =~ ${OverlayExcludes} ]] && continue
 			local name="${mod%/*}"
 			local add='no'
 			if [[ -n "${ol}" && "${ol}" != 'none' ]]; then