Add test for KT-49209

compiler/testData/codegen/box/platformTypes/kt49209.kt

@@ -0,0 +1,12 @@
+// TARGET_BACKEND: JVM
+// IGNORE_BACKEND_FIR: JVM_IR
+// JVM_TARGET: 1.8
+// FULL_JDK
+
+import java.util.Optional
+
+fun <T> T?.toOptional(): Optional<T> = Optional.ofNullable(this)
+
+fun box(): String {
+    return "OK".toOptional().get()
+}