updateConfigEntry: Fix sed expanding escape sequences

Related to #1072.

Stop sed from expanding escape sequences in strings.
This function is used to save config entry items, and
sed is expanding any backslashes in these options.

There should never really be a case where we want
config entry values to be expanded in this way,
and also this is causing problems in #1072 where
Windows paths using backslashes are mangled on
initial save.

Modify the sed command to use single-quotes for
sed-specific syntax, and double quotes for
variables, so they won't get expanded.

This modifies an EXTREMELY core part of STL, so
it will need extensive testing before it can be
merged.

steamtinkerlaunch

@@ -7,7 +7,7 @@
 PREFIX="/usr"
 PROGNAME="SteamTinkerLaunch"
 NICEPROGNAME="Steam Tinker Launch"
-PROGVERS="v14.0.20240323-1"
+PROGVERS="v14.0.20240324-1 (updateConfigEntry-sed-prevent-escaping)"
 PROGCMD="${0##*/}"
 PROGINTERNALPROTNAME="Proton-stl"
 SHOSTL="stl"
@@ -10921,17 +10921,24 @@ function updateConfigEntry {
 				fi
 
 				# only save value if it changed
+				#
+				# NOTE 24/03/2024 - the  sed command was changed to prevent expanding escape sequences,
+				# i.e. removing backslashes from Windows paths, or interpreting `\t` as a tab character.
+				# please report if this causes problems!
 				if { [ "${!CFGCAT}" != "$CFGVALUE" ] && [ "${!CFGCAT}" != "${CFGVALUE//$STLCFGDIR/STLCFGDIR}" ];} || [ -f "$FUPDATE" ]; then
 					CFGVALUE="${CFGVALUE//$STLCFGDIR/STLCFGDIR}"
 					if [ "$(grep -c "#${CFGCAT}=" "$CFGFILE")" -eq 1 ]; then
 						writelog "INFO" "${FUNCNAME[0]} - Option '$CFGCAT' commented out in config '${CFGFILE##*/}' - activating it with the new value '$CFGVALUE'"
-						sed -i "/^#${CFGCAT}=/c$CFGCAT=\"$CFGVALUE\"" "$CFGFILE"
+						# sed -i "/^#${CFGCAT}=/c$CFGCAT=\"$CFGVALUE\"" "$CFGFILE"
+						sed -i '/^#'"${CFGCAT}"'=/c\'"${CFGCAT}=\"$CFGVALUE\"" "$CFGFILE"
 					elif [ "$(grep -c "^${CFGCAT}=" "$CFGFILE")" -eq 0 ]; then
 						writelog "INFO" "${FUNCNAME[0]} - '$CFGCAT' option missing in config '${CFGFILE##*/}' - adding a new line"
-						echo "$CFGCAT=\"$CFGVALUE\"" >> "$CFGFILE"
+						# echo "$CFGCAT=\"$CFGVALUE\"" >> "$CFGFILE"
+						printf "%s=\"%s\"\n" "${CFGCAT}" "${CFGVALUE}" >> "${CFGFILE}"
 					else
 						writelog "INFO" "${FUNCNAME[0]} - Option '$CFGCAT' is updated with the new value '$CFGVALUE' in config '${CFGFILE##*/}'"
-						sed -i "/^${CFGCAT}=/c$CFGCAT=\"$CFGVALUE\"" "$CFGFILE"
+						# sed -i "/^${CFGCAT}=/c$CFGCAT=\"$CFGVALUE\"" "$CFGFILE"
+						sed -i '/^'"${CFGCAT}"'=/c\'"${CFGCAT}=\"$CFGVALUE\"" "$CFGFILE"
 					fi
 					rm "$FUPDATE" 2>/dev/null
 				fi