usrmount/mount-usr.sh: give emergency_shell if /usr mount failed

modules.d/98usrmount/mount-usr.sh

@@ -74,10 +74,9 @@ mount_usr()
             if [ "0" != "${_passno:-0}" ]; then
                 fsck_usr "$_dev" "$_fs" "$_opts"
                 _fsck_ret=$?
-                echo $_fsck_ret >/run/initramfs/usr-fsck
+                [ $_fsck_ret -ne 255 ] && echo $_fsck_ret >/run/initramfs/usr-fsck
             fi
         fi
-        if [ $_fsck_ret -ne 255 ]; then
         if getargbool 0 rd.usrmount.ro; then
             info "Mounting /usr (read-only forced)"
             mount -r "$NEWROOT/usr" 2>&1 | vinfo
@@ -85,6 +84,11 @@ mount_usr()
             info "Mounting /usr"
             mount "$NEWROOT/usr" 2>&1 | vinfo
         fi
+        if ! ismounted /usr; then
+            warn "Mounting /usr to $NEWROOT/usr failed"
+            warn "*** Dropping you to a shell; the system will continue"
+            warn "*** when you leave the shell."
+            emergency_shell
         fi
     fi
 }