check texlists at map load

if by some freak accident the list gets corrupted, the textures are no
longer accessible from the map editor

this check makes sure, that nothing is missing

source/src/worldio.cpp

@@ -318,6 +318,25 @@ extern char *mlayout;
 extern int Mv, Ma, Hhits;
 extern float Mh;
 
+void rebuildtexlists()  // checks the texlists, if they still contain all possible textures
+{
+    short h[256];
+    vector<uchar> missing;
+    loopk(3)
+    {
+        missing.setsize(0);
+        uchar *p = hdr.texlists[k];
+        loopi(256) h[i] = 0;
+        loopi(256) h[p[i]]++;
+        loopi(256) if(h[i] == 0) missing.add(i);
+        loopi(256) if(h[p[i]] > 1)
+        {
+            h[p[i]]--;
+            p[i] = missing.pop();
+        }
+    }
+}
+
 bool load_world(char *mname)        // still supports all map formats that have existed since the earliest cube betas!
 {
     const int sizeof_header = sizeof(header), sizeof_baseheader = sizeof_header - sizeof(int) * 16;
@@ -364,6 +383,7 @@ bool load_world(char *mname)        // still supports all map formats that have
         f->seek(tmp.headersize - sizeof_header - headerextrasize, SEEK_CUR);  // (equivalent to SEEK_SET to tmp.headersize)
     }
     hdr = tmp;
+    rebuildtexlists();
     loadingscreen("%s", hdr.maptitle);
     resetmap();
     if(hdr.version>=4)