[C] Correct positions for created Fires in EntityLightning. Fixes BUKKIT-4707

<b>The Issue:</b>
Lightning strikes caused fires to appear at the wrong positions, because some variables were interchanged. This could damage maps, because any block (not only air) could be replaced by fires.

<b>Justification for this PR:</b>
Without this fix maps are damaged by replacing the wrong blocks by fire.

<b>PR Breakdown:</b>
This commit fixes this issue by using the correct variables.

<b>JIRA Ticket:</b>
BUKKIT-4707 - https://bukkit.atlassian.net/browse/BUKKIT-4707