Fix for 'if' special construct type

If one branch has Nothing type (contains 'return', etc.),
return result type of corresponding resolved call (it may depend on smart casts)
 #KT-6242 Fixed

compiler/testData/diagnostics/tests/smartCasts/inference/kt6242.txt

@@ -0,0 +1,4 @@
+package
+
+internal fun baz(): kotlin.Unit
+kotlin.inline() internal fun </*0*/ T> foo(/*0*/ block: () -> T): T