[FIR] Harden check of argument type properly

Before this commit, nullable argument could match not null parameter.
Now we require also correct nullability that breaks some cases

compiler/testData/diagnostics/tests/extensions/kt1875.fir.kt

@@ -3,7 +3,7 @@
 
 package kt1875
 
-fun foo(a : Int?, b : Int.(Int)->Int) = a?.b(1) //unnecessary safe call warning
+fun foo(a : Int?, b : Int.(Int)->Int) = a?.<!INAPPLICABLE_CANDIDATE!>b<!>(1) //unnecessary safe call warning
 
 interface T {
     val f : ((i: Int) -> Unit)?