Config: Fixes string enum parser with multiple arguments

Messed up when originally implementing this, substr's second argument is
requested substring length, not the ending position.

Noticed this while trying to parse multiple FEX_HOSTFEATURES options.

FEXCore/include/FEXCore/Config/Config.h

@@ -118,7 +118,7 @@ namespace Handler {
       }
       Begin = End + 1;
       End = View.find_first_of(',', Begin);
-      Option = View.substr(Begin, End);
+      Option = View.substr(Begin, End - Begin);
     }
 
     return fextl::fmt::format("{}", EnumMask);