Fix aliens being selectable by default (#900)

Broken in 6a382830a9
This change also allows you to make selectable insects with selectable=1 in scene file

src/object/old_object.cpp

@@ -1041,7 +1041,7 @@ void COldObject::Read(CLevelParserLine* line)
     SetAnimateOnReset(line->GetParam("reset")->AsBool(false));
     if (Implements(ObjectInterfaceType::Controllable))
     {
-        SetSelectable(line->GetParam("selectable")->AsBool(true));
+        SetSelectable(line->GetParam("selectable")->AsBool(IsSelectableByDefault(m_type)));
     }
     if (Implements(ObjectInterfaceType::JetFlying))
     {
@@ -3174,3 +3174,17 @@ float COldObject::GetLightningHitProbability()
     }
     return 0.0f;
 }
+
+bool COldObject::IsSelectableByDefault(ObjectType type)
+{
+    if ( type == OBJECT_MOTHER   ||
+         type == OBJECT_ANT      ||
+         type == OBJECT_SPIDER   ||
+         type == OBJECT_BEE      ||
+         type == OBJECT_WORM     ||
+         type == OBJECT_MOBILEtg )
+    {
+        return false;
+    }
+    return true;
+}

src/object/old_object.h

@@ -302,6 +302,12 @@ protected:
     void        TransformCrashSphere(Math::Sphere &crashSphere) override;
     void TransformCameraCollisionSphere(Math::Sphere& collisionSphere) override;
 
+    /**
+     * \brief Check if given object type should be selectable by default
+     * \note This is a default value for the selectable= parameter and can still be overriden in the scene file or using the \a selectinsect cheat
+     */
+    static bool IsSelectableByDefault(ObjectType type);
+
 protected:
     Gfx::CEngine*       m_engine;
     Gfx::CLightManager* m_lightMan;