fix(suse-initrd): handle cases with zero modprobe.d files

If get_modprobe_conf_files() returns nothing (no modprobe.d file
installed on the system), the grep command in installkernel() hangs.
Fix it. Fixes bsc#1189895.

Author: mwilck

modules.d/99suse-initrd/module-setup.sh

@@ -10,7 +10,8 @@
 # called by dracut
 check() {
     # Skip the module if no SUSE INITRD is used
-    grep -q "^# SUSE INITRD: " $(get_modprobe_conf_files)
+    local conf_files=$(get_modprobe_conf_files)
+    [[ $conf_files ]] && grep -q "^# SUSE INITRD: " $conf_files
 }
 
 get_modprobe_conf_files() {
@@ -20,6 +21,11 @@ get_modprobe_conf_files() {
     return 0
 }
 
+get_suse_initrd_lines() {
+    local conf_files=$(get_modprobe_conf_files)
+    [[ -z "$conf_files" ]] || grep -h "^# SUSE INITRD: " $conf_files
+}
+
 read_initrd_modules() {
     if [[ -f /etc/sysconfig/kernel ]]; then
         INITRD_MODULES=
@@ -47,7 +53,7 @@ installkernel() {
         then
             all_mods="$all_mods $(filter_builtin $reqs)"
         fi
-    done <<< "$(grep -h "^# SUSE INITRD: " $(get_modprobe_conf_files))"
+    done <<< "$(get_suse_initrd_lines)"
 
     # strip whitespace
     all_mods="$(echo $all_mods)"