test_ltface.cc: add assertions to catch command line options leaking

across tests

common/bsputils.cc

@@ -923,6 +923,8 @@ qvec3b LM_Sample(const mbsp_t *bsp, const faceextents_t &faceextents, int byte_o
 {
     int pixel = coord[0] + (coord[1] * faceextents.width());
 
+    assert(byte_offset_of_face >= 0);
+
     const uint8_t* data = bsp->dlightdata.data();
 
     if (bsp->loadversion->game->has_rgb_lightmap) {

tests/test_ltface.cc

@@ -150,6 +150,7 @@ TEST_CASE("-novanilla + -world_units_per_luxel")
 
 TEST_CASE("emissive lights") {
     auto [bsp, bspx] = LoadTestmap("q2_light_flush.map", {});
+    REQUIRE(bspx.empty());
 
     // all of this face should be receiving some light
     auto *face = BSP_FindFaceAtPoint(&bsp, &bsp.dmodels[0], {244, -92, 92});