JVM_IR simplify null check on trivially initialized vals only

compiler/testData/codegen/box/safeCall/safeCallIOnUninitializedNonNullValue.kt

@@ -0,0 +1,18 @@
+abstract class Base() {
+    init {
+        foo()
+    }
+
+    abstract fun foo()
+}
+
+class Derived(val x: String) : Base() {
+    override fun foo() {
+        x?.length
+    }
+}
+
+fun box(): String {
+    Derived("")
+    return "OK"
+}