Fixx out-of-range access in ASE-Parser

- closes https://github.com/assimp/assimp/issues/4495

code/AssetLib/ASE/ASEParser.cpp

@@ -646,7 +646,9 @@ void Parser::ParseLV2MaterialBlock(ASE::Material &mat) {
                 }
 
                 // get a reference to the material
+                if (iIndex < mat.avSubMaterials.size()) {
                     Material &sMat = mat.avSubMaterials[iIndex];
+                }
 
                 // parse the material block
                 ParseLV2MaterialBlock(sMat);