fix(xnt): derive sha512 URL from remotebuildfilename not remotebuildtag

Tag format is xonotic-v0.8.6 but the sha512 file is named xonotic-0.8.6.sha512
(without the v). Using remotebuildtag directly produced a 404. Deriving from
remotebuildfilename (which already has the v stripped by tr -d v) gives the
correct URL.

lgsm/modules/update_xnt.sh

@@ -55,7 +55,7 @@ fn_update_remotebuild() {
 	remotebuildfilename="${remotebuildfilename}.zip"
 	remotebuildurl="https://dl.xonotic.org/${remotebuildfilename}"
 	remotebuild="${remotebuildtag}"
-	remotebuildhash=$(curl -s "https://dl.xonotic.org/${remotebuildtag}.sha512" | grep "${remotebuildfilename}$" | grep -oE '[a-f0-9]{128}')
+	remotebuildhash=$(curl -s "https://dl.xonotic.org/${remotebuildfilename%.zip}.sha512" | grep "${remotebuildfilename}$" | grep -oE '[a-f0-9]{128}')
 
 	if [ "${firstcommandname}" != "INSTALL" ]; then
 		fn_print_dots "Checking remote build: ${remotelocation}"