SceneGraph: test crash and burn when deleting a running animable.

Yes. It does.

src/Magnum/SceneGraph/Test/AnimableTest.cpp

@@ -42,6 +42,8 @@ struct AnimableTest: TestSuite::Tester {
     void stop();
     void pause();
 
+    void deleteWhileRunning();
+
     void debug();
 };
 
@@ -55,6 +57,8 @@ AnimableTest::AnimableTest() {
               &AnimableTest::stop,
               &AnimableTest::pause,
 
+              &AnimableTest::deleteWhileRunning,
+
               &AnimableTest::debug});
 }
 
@@ -351,6 +355,28 @@ void AnimableTest::pause() {
     CORRADE_COMPARE(animable.time, 2.0f);
 }
 
+void AnimableTest::deleteWhileRunning() {
+    Object3D object;
+    AnimableGroup3D group;
+    CORRADE_COMPARE(group.runningCount(), 0);
+
+    {
+        OneShotAnimable animable(object, &group);
+
+        /* Eat up some absolute time */
+        group.step(1.0f, 0.5f);
+        group.step(1.5f, 0.5f);
+        CORRADE_COMPARE(group.runningCount(), 1);
+
+        CORRADE_COMPARE(animable.state(), AnimationState::Running);
+        CORRADE_COMPARE(animable.time, 0.5f);
+    }
+
+    /* Animable got deleted, stepping further should not crash and burn (tm) */
+    group.step(1.5f, 0.5f);
+    CORRADE_COMPARE(group.runningCount(), 0);
+}
+
 void AnimableTest::debug() {
     std::ostringstream o;
     Debug(&o) << AnimationState::Running << AnimationState(0xbe);