KT-52743 IR: Fix null checks in Elvis operators

compiler/testData/codegen/box/safeCall/kt52743.kt

@@ -0,0 +1,8 @@
+fun <T: Any?> nullableFun(): T {
+    return null as T
+}
+
+fun box(): String {
+    val t = nullableFun<String>()
+    return if (t?.length == null) "OK" else "Fail"
+}