Kotlin: Add test for useless null check on safe calls

java/ql/test/kotlin/query-tests/UselessNullCheck/Test.kt

@@ -9,3 +9,10 @@ fun fn(x:Any?, y: Any?) {
         println("y not null")
     }
 }
+
+fun fn0(o: Any?) {
+    if (o != null) {
+        o?.toString()
+        o.toString()
+    }
+}

java/ql/test/kotlin/query-tests/UselessNullCheck/UselessNullCheck.expected

@@ -0,0 +1 @@
+| Test.kt:15:12:15:21 | ... (value equals) ... | This check is useless. $@ cannot be null at this check, since it is guarded by $@. | Test.kt:15:9:15:9 | tmp0_safe_receiver | tmp0_safe_receiver | Test.kt:14:9:14:17 | ... (value not-equals) ... | ... (value not-equals) ... |