Fix for engines that require edges reference valid vertices (edge 0 references vertex 0 but it might not be set in some cases)

Change `Brush_GetContents` again so that clip works

qbsp/brush.cc

@@ -668,14 +668,13 @@ static contentflags_t Brush_GetContents(const mapbrush_t *mapbrush)
     for (int i = 0; i < mapbrush->numfaces; i++) {
         const mapface_t &mapface = mapbrush->face(i);
         const mtexinfo_t &texinfo = map.mtexinfos.at(mapface.texinfo);
+        contentflags_t contents = options.target_game->face_get_contents(mapface.texname.data(), texinfo.flags, mapface.contents);
 
-        if (texinfo.flags.is_skip) {
+        if (contents.is_empty(options.target_game)) {
             continue;
         }
-
-        contentflags_t contents = options.target_game->face_get_contents(mapface.texname.data(), texinfo.flags, mapface.contents);
         
-        // use the first non-skip as the base contents value
+        // use the first non-empty as the base contents value
         if (!base_contents_set) {
             base_contents_set = true;
             base_contents = contents;

qbsp/writebsp.cc

@@ -439,6 +439,12 @@ void FinishBSPFile(void)
     options.fVerbose = true;
     LogPrint(LOG_PROGRESS, "---- {} ----\n", __func__);
 
+    if (map.bsp.dvertexes.empty()) {
+        // First vertex must remain unused because edge references it
+        map.bsp.dvertexes.emplace_back();
+        Q_assert(map.bsp.dvertexes.size() == 1);
+    }
+
     WriteExtendedTexinfoFlags();
     WriteBSPFile();