[sldev] fix for the distortion when zooming out with ctrl 8 bug

[Khyota]

http://jira.secondlife.com/browse/VWR-5241

Me and Carjay McGinnis worked on this tonight. Zoom out this way changes the 
field of vision by 20%, the default being 60 degrees. When it starts getting 
closer to 180 degrees the view gets extremely distorted. The 6th increment 
puts it at 179.159 and causes a nasty image, the 7th puts it at 180 because 
thats ware the maximum is set, PI radians. Seeing that the minimum was set 
for 0.1rad i set the maximum for 0.9*PI rad and it causes no distortion.

This was a really simple fix and i hope it can get imported quickly.