Avoid object's interpretation with nullable type

#KT-56215 Fixed

compiler/testData/codegen/box/involvesIrInterpreter/kt56215.kt

@@ -0,0 +1,22 @@
+object ObjectWithExtension
+
+fun ObjectWithExtension?.nullableExtensionFun(): String =
+    if(this == null)
+        "Null"
+    else
+        "Not null"
+
+fun ObjectWithExtension.extensionFun(): String =
+    if(this == null)
+        "Null" // unreachable branch, will be optimized by interpreter
+    else
+        "Not null"
+
+fun box(): String {
+    val nullObjectWithExtension: ObjectWithExtension? = null
+    if ("${nullObjectWithExtension.nullableExtensionFun()}" != "Null") return "Fail 1"
+    if ("${ObjectWithExtension.nullableExtensionFun()}" != "Not null") return "Fail 2"
+
+    if ("${ObjectWithExtension.extensionFun()}" != "Not null") return "Fail 3"
+    return "OK"
+}