Groundcover should ignore non-geometry Drawables

Fix https://gitlab.com/OpenMW/openmw/-/issues/7633

Untested - the issue didn't link to a mod using the mesh and I couldn't be bothered setting one up manually.

CHANGELOG.md

@@ -111,6 +111,7 @@
     Bug #7619: Long map notes may get cut off
     Bug #7630: Charm can be cast on creatures
     Bug #7631: Cannot trade with/talk to Creeper or Mudcrab Merchant when they're fleeing
+    Bug #7633: Groundcover should ignore non-geometry Drawables
     Bug #7636: Animations bug out when switching between 1st and 3rd person, while playing a scripted animation
     Bug #7637: Actors can sometimes move while playing scripted animations
     Bug #7639: NPCs don't use hand-to-hand if their other melee skills were damaged during combat

apps/openmw/mwrender/groundcover.cpp

@@ -196,6 +196,18 @@ namespace MWRender
             {
             }
 
+            void apply(osg::Group& group) override
+            {
+                for (unsigned int i = 0; i < group.getNumChildren();)
+                {
+                    if (group.getChild(i)->asDrawable() && !group.getChild(i)->asGeometry())
+                        group.removeChild(i);
+                    else
+                        ++i;
+                }
+                traverse(group);
+            }
+
             void apply(osg::Geometry& geom) override
             {
                 for (unsigned int i = 0; i < geom.getNumPrimitiveSets(); ++i)