gparam: Remove unnecessary conditionals around preconditions
gparam: Remove unnecessary conditionals around preconditions

These cause a static analyzer to think we're trying to actually handle
them being NULL, which is not the case.  They both must not be NULL,
period.

No idea why the code was like this originally.

Reviewed by mclasen on IRC.

lukasz-skalski/glib,krichter722/glib,johne53/MB3Glib,Distrotech/glib,tchakabam/glib,gale320/glib,cention-sany/glib,krichter722/glib,cention-sany/glib,tchakabam/glib,lukasz-skalski/glib,lukasz-skalski/glib,ieei/glib,tamaskenez/glib,tchakabam/glib,MathieuDuponchelle/glib,ieei/glib,krichter722/glib,MathieuDuponchelle/glib,cention-sany/glib,Distrotech/glib,tchakabam/glib,Distrotech/glib,tamaskenez/glib,krichter722/glib,lukasz-skalski/glib,ieei/glib,mzabaluev/glib,tamaskenez/glib,johne53/MB3Glib,mzabaluev/glib,MathieuDuponchelle/glib,tamaskenez/glib,endlessm/glib,krichter722/glib,gale320/glib,endlessm/glib,MathieuDuponchelle/glib,Distrotech/glib,MathieuDuponchelle/glib,johne53/MB3Glib,cention-sany/glib,mzabaluev/glib,gale320/glib,gale320/glib,Distrotech/glib,cention-sany/glib,tchakabam/glib,johne53/MB3Glib,tamaskenez/glib,gale320/glib,johne53/MB3Glib,ieei/glib,mzabaluev/glib,ieei/glib,endlessm/glib,endlessm/glib,mzabaluev/glib,johne53/MB3Glib,lukasz-skalski/glib,endlessm/glib