map_galaxy.php: fix missing FontSize variable
map_galaxy.php: fix missing FontSize variable

When FontSize was made a separate variable in Head.inc, it was
not added as a template variable for all pages that include
Head.inc, which resulted in an undefined variable warning.

We use `getFontSize() - 20` for the map_galaxy.php value for
consistency with the main game pages.

hemberger/smr,hemberger/smr,hemberger/smr,hemberger/smr,smrealms/smr,smrealms/smr,smrealms/smr