KT-9835 Completion thinks receiver is nullable when it is not

#KT-9835 Fixed

idea/idea-completion/testData/basic/common/boldOrGrayed/KT9835.kt

@@ -0,0 +1,15 @@
+interface R<T>
+
+val <T> R<T>.prop: Int get() = TODO()
+fun <T> R<T>.extFun(): Int = TODO()
+
+interface I
+
+fun foo(r: R<out I>) {
+    r.<caret>
+}
+
+// EXIST: { itemText: "prop", typeText: "Int", attributes: "bold" }
+// EXIST: { itemText: "extFun", typeText: "Int", attributes: "bold" }
+
+