kdump-lib-initramfs: harden is_mounted

If the device/mountpoint for findmnt is omitted findmnt will list all
mounted filesystems. In that case it will always return "true". So
explicitly check if an argument was passed to prevent false-positives.

Signed-off-by: Philipp Rudo <prudo@redhat.com>
Reviewed-by: Coiby Xu <coxu@redhat.com>

kdump-lib-initramfs.sh

@@ -30,7 +30,7 @@ kdump_get_conf_val()
 
 is_mounted()
 {
-	findmnt -k -n "$1" > /dev/null 2>&1
+	[ -n "$1" ] && findmnt -k -n "$1" > /dev/null 2>&1
 }
 
 # $1: info type