fix some index out of bounds by requiring initial disks in file board source

This causes some UB in the end solver and the game is not ready for this case for multiple reasons - lot of routines assume only 60 moves or that initial disks are not empty.

Author: panstromek

game.c

@@ -260,6 +260,10 @@ setup_game( const char *file_name, int *side_to_move ) {
     else
       fatal_error( "%s '%c' %s\n", BAD_CHARACTER_ERROR, buffer[0],
 		   GAME_FILE_TEXT);
+    if (board[45] == EMPTY || board[54] == EMPTY || board[44] == EMPTY || board[55] == EMPTY) {
+        // various pieces of the program are not ready for this, even though we have end solve routines for it
+        fatal_error( "Initial squares (d4, e4, d5, e5) from the board file should not be empty.\n");
+    }
   }
   disks_played = disc_count( BLACKSQ ) + disc_count( WHITESQ ) - 4;