[FIR] Fix false-positive smartcast on receiver in rhs of elvis

#KT-44942 Fixed

compiler/testData/codegen/box/smartCasts/kt44942.kt

@@ -0,0 +1,19 @@
+// ISSUE: KT-44942
+
+abstract class A {
+    abstract fun foo(): String
+}
+
+class B : A() {
+    override fun foo(): String = "fail"
+
+    fun bar() = "fail"
+}
+
+class C : A() {
+    override fun foo(): String = "OK"
+}
+
+fun A.test() = (this as? B)?.bar() ?: foo()
+
+fun box() = C().test()