[AST] NFC: Avoid nullptr comparisons
[AST] NFC: Avoid nullptr comparisons

There is some worry in GitHub PR #13795 that future compilers might
optimize away the whole assert because of the nullptr comparison.

jmgc/swift,CodaFi/swift,natecook1000/swift,glessard/swift,sschiau/swift,practicalswift/swift,glessard/swift,stephentyrone/swift,brentdax/swift,glessard/swift,danielmartin/swift,huonw/swift,ahoppen/swift,apple/swift,parkera/swift,sschiau/swift,xwu/swift,karwa/swift,shajrawi/swift,tjw/swift,aschwaighofer/swift,stephentyrone/swift,allevato/swift,atrick/swift,ahoppen/swift,lorentey/swift,parkera/swift,sschiau/swift,apple/swift,huonw/swift,jmgc/swift,JGiola/swift,karwa/swift,zisko/swift,CodaFi/swift,roambotics/swift,brentdax/swift,harlanhaskins/swift,shahmishal/swift,devincoughlin/swift,harlanhaskins/swift,CodaFi/swift,hooman/swift,xedin/swift,shajrawi/swift,aschwaighofer/swift,devincoughlin/swift,parkera/swift,danielmartin/swift,tkremenek/swift,harlanhaskins/swift,natecook1000/swift,harlanhaskins/swift,jckarter/swift,jmgc/swift,xwu/swift,benlangmuir/swift,CodaFi/swift,hooman/swift,brentdax/swift,airspeedswift/swift,amraboelela/swift,zisko/swift,xedin/swift,tjw/swift,tkremenek/swift,benlangmuir/swift,CodaFi/swift,lorentey/swift,shahmishal/swift,jckarter/swift,sschiau/swift,tkremenek/swift,natecook1000/swift,allevato/swift,harlanhaskins/swift,gribozavr/swift,stephentyrone/swift,lorentey/swift,lorentey/swift,jopamer/swift,shahmishal/swift,sschiau/swift,JGiola/swift,ahoppen/swift,sschiau/swift,tkremenek/swift,zisko/swift,practicalswift/swift,gribozavr/swift,jckarter/swift,shajrawi/swift,roambotics/swift,austinzheng/swift,jopamer/swift,allevato/swift,amraboelela/swift,JGiola/swift,tjw/swift,apple/swift,hooman/swift,JGiola/swift,apple/swift,jmgc/swift,jopamer/swift,brentdax/swift,danielmartin/swift,benlangmuir/swift,shajrawi/swift,huonw/swift,roambotics/swift,shahmishal/swift,hooman/swift,shajrawi/swift,xedin/swift,devincoughlin/swift,glessard/swift,xedin/swift,amraboelela/swift,jckarter/swift,parkera/swift,karwa/swift,jopamer/swift,nathawes/swift,devincoughlin/swift,parkera/swift,airspeedswift/swift,danielmartin/swift,roambotics/swift,shahmishal/swift,austinzheng/swift,alblue/swift,xedin/swift,airspeedswift/swift,stephentyrone/swift,harlanhaskins/swift,danielmartin/swift,alblue/swift,karwa/swift,shahmishal/swift,karwa/swift,parkera/swift,harlanhaskins/swift,glessard/swift,gribozavr/swift,JGiola/swift,ahoppen/swift,natecook1000/swift,gregomni/swift,rudkx/swift,gregomni/swift,alblue/swift,sschiau/swift,allevato/swift,brentdax/swift,gribozavr/swift,zisko/swift,xwu/swift,roambotics/swift,alblue/swift,natecook1000/swift,huonw/swift,zisko/swift,huonw/swift,tjw/swift,allevato/swift,CodaFi/swift,alblue/swift,huonw/swift,practicalswift/swift,gregomni/swift,aschwaighofer/swift,allevato/swift,benlangmuir/swift,lorentey/swift,airspeedswift/swift,xwu/swift,gribozavr/swift,aschwaighofer/swift,karwa/swift,alblue/swift,hooman/swift,jmgc/swift,austinzheng/swift,jmgc/swift,parkera/swift,rudkx/swift,amraboelela/swift,atrick/swift,atrick/swift,jopamer/swift,xedin/swift,airspeedswift/swift,gribozavr/swift,gregomni/swift,nathawes/swift,austinzheng/swift,alblue/swift,shahmishal/swift,ahoppen/swift,gregomni/swift,atrick/swift,CodaFi/swift,hooman/swift,danielmartin/swift,aschwaighofer/swift,xedin/swift,practicalswift/swift,karwa/swift,gribozavr/swift,gregomni/swift,rudkx/swift,rudkx/swift,tjw/swift,shajrawi/swift,tkremenek/swift,parkera/swift,tjw/swift,allevato/swift,JGiola/swift,jckarter/swift,hooman/swift,rudkx/swift,danielmartin/swift,zisko/swift,natecook1000/swift,benlangmuir/swift,jopamer/swift,lorentey/swift,devincoughlin/swift,austinzheng/swift,natecook1000/swift,austinzheng/swift,gribozavr/swift,roambotics/swift,stephentyrone/swift,benlangmuir/swift,karwa/swift,practicalswift/swift,nathawes/swift,aschwaighofer/swift,jopamer/swift,rudkx/swift,xwu/swift,nathawes/swift,jckarter/swift,shajrawi/swift,atrick/swift,stephentyrone/swift,tjw/swift,lorentey/swift,practicalswift/swift,apple/swift,brentdax/swift,apple/swift,devincoughlin/swift,tkremenek/swift,ahoppen/swift,airspeedswift/swift,xwu/swift,austinzheng/swift,atrick/swift,jckarter/swift,shajrawi/swift,sschiau/swift,nathawes/swift,tkremenek/swift,nathawes/swift,aschwaighofer/swift,amraboelela/swift,devincoughlin/swift,lorentey/swift,brentdax/swift,stephentyrone/swift,xwu/swift,jmgc/swift,practicalswift/swift,airspeedswift/swift,huonw/swift,zisko/swift,xedin/swift,amraboelela/swift,practicalswift/swift,shahmishal/swift,nathawes/swift,devincoughlin/swift,amraboelela/swift,glessard/swift