[FIR2IR] Don't create f/o symbols on smartcasted Nothing in dispatch receiver

^KT-63525 Fixed

compiler/testData/codegen/box/controlflow/callOnSmarcastedNothing.kt

@@ -0,0 +1,14 @@
+// ISSUE: KT-63525
+
+fun box(): String {
+    var b: String? = "abc"
+    b = null
+    var x = 0
+    if (b != null) {
+        x += b.length
+    }
+    return when (x) {
+        0 -> "OK"
+        else -> "Fail: $x"
+    }
+}