Kotlin: Add test for NullMaybe query

Author: tamasvajk

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

@@ -0,0 +1 @@
+| Test.kt:6:13:6:13 | d | Variable $@ may be null here because of $@ assignment. | Test.kt:2:5:2:25 | Double d | d | Test.kt:2:5:2:25 | d | this |

java/ql/test/kotlin/query-tests/NullMaybe/NullMaybe.qlref

@@ -0,0 +1 @@
+Likely Bugs/Nullness/NullMaybe.ql

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

@@ -0,0 +1,7 @@
+fun fn(b: Boolean) {
+    var d: Double? = null
+    if (b) {
+        d = 1.0
+    }
+    println(d!!)
+}