Fix nullability check (in case of explicitly nullable types constructed from ype variables)

compiler/testData/codegen/notNullAssertions/noAssertionForNullableGenericMethodCall.kt

@@ -0,0 +1,7 @@
+import java.util.HashMap
+
+class A<T: Any> {
+    fun main() {
+        HashMap<String, T>()[""]
+    }
+}