Remove redundant null check in Pair.cs.
Remove redundant null check in Pair.cs.

'is' will return false if it is null in this case (as it isn't a Pair in that case)

blue3k/ATF,gelahcem/ATF,gelahcem/ATF,mindbaffle/ATF,jethac/ATF,mindbaffle/ATF,Nuclearfossil/ATF,dogdirt2000/ATF,dogdirt2000/ATF,JSandusky/ATF,blue3k/ATF,dogdirt2000/ATF,jethac/ATF,blue3k/ATF,jethac/ATF,mszymczyk/ATF,JSandusky/ATF,Nuclearfossil/ATF,mszymczyk/ATF,JSandusky/ATF,gelahcem/ATF,twainj/ATF,gelahcem/ATF,mindbaffle/ATF,SonyWWS/ATF,gelahcem/ATF,blue3k/ATF,SonyWWS/ATF,jethac/ATF,blue3k/ATF,mszymczyk/ATF,SonyWWS/ATF,dogdirt2000/ATF,jethac/ATF,mszymczyk/ATF,mszymczyk/ATF,JSandusky/ATF,dogdirt2000/ATF,JSandusky/ATF,Nuclearfossil/ATF,twainj/ATF,twainj/ATF,SonyWWS/ATF,twainj/ATF,twainj/ATF,SonyWWS/ATF