Refactor logic which checks for too large allocations

It's now easier to change the limit

code/ObjFileImporter.cpp

@@ -382,7 +382,7 @@ void ObjFileImporter::createVertexArray(const ObjFile::Model* pModel,
     pMesh->mNumVertices = numIndices;
     if (pMesh->mNumVertices == 0) {
         throw DeadlyImportError( "OBJ: no vertices" );
-    } else if (pMesh->mNumVertices > std::numeric_limits<int32_t>::max() / sizeof(aiVector3D)) {
+    } else if (pMesh->mNumVertices > AI_MAX_ALLOC(aiVector3D)) {
         throw DeadlyImportError( "OBJ: Too many vertices, would run out of memory" );
     }
     pMesh->mVertices = new aiVector3D[ pMesh->mNumVertices ];