Fix generation of elvis with null constant for inline classes

compiler/testData/codegen/bytecodeText/inlineClasses/boxInlineClassInsideElvisWithNullConstant.kt

@@ -0,0 +1,13 @@
+// !LANGUAGE: +InlineClasses
+
+inline class UInt(private val data: Int)
+
+fun f() {
+    val unull = UInt(1) ?: null
+}
+
+// 1 INVOKESTATIC UInt\$Erased.box
+// 0 INVOKEVIRTUAL UInt.unbox
+
+// 0 valueOf
+// 0 intValue