When set to 0.5, menu setting r_water_resolutionmultiplier is not saved to config.cfg

Hello,

I know it sounds weird, but when "r_water_resolutionmultiplier" cvar is set to "0.5" (with the console or through the menu on Settings -> Effects -> Reflections -> "Good"), it's not saved to config.cfg. On next Xonotic relaunch, this cvar will be reverted back to 0.25 ("Blurred" value on menu).

If the value is set to something else than 0.5, it will be saved to config.cfg (I tried with 1, 0.6, 0.4, and even 0.50 works) as expected.

Tested with 12/31/14 autobuild on Linux.