add a bool parameter to allow forced reindexation of a mesh

src/osgUtil/MeshOptimizers.cpp

@@ -262,7 +262,7 @@ void IndexMeshVisitor::makeMesh(Geometry& geom)
     }
 
     // nothing to index
-    if (!numSurfacePrimitives || !numNonIndexedPrimitives) return;
+    if (!numSurfacePrimitives || (!_isForcedReindexationEnable && !numNonIndexedPrimitives)) return;
 
     // duplicate shared arrays as it isn't safe to rearrange vertices when arrays are shared.
     if (geom.containsSharedArrays()) geom.duplicateSharedArrays();