Fix funcs not being reassigned if delta func is last func in list

One of the solutions to the quit signal unfocus pause regression is to
add a no-op delta func to the unfocused func table. However, this
results in the game being stuck in unfocus pause forever, because when
it reaches the end of a list on a delta func, it won't reassign the
active functions - only when the end of a list is a fixed func will it
do so. A workaround is to then add a no-op fixed func afterwards, but
that's inelegant.

The solution in the end to the quit signal regression is to not bother
with adding a delta func, so the game as of right now actually never has
a delta func at the end of a list, and probably never will - but this is
one piece of technical debt I don't want to leave laying around. In case
we're ever going to put a delta function at the end of a list, I've made
it so that delta functions will now reassign the list of active funcs if
they happen to be at the end of the func list.

desktop_version/src/main.cpp

@@ -681,7 +681,12 @@ static void inline deltaloop(void)
 
     while (accumulator >= timesteplimit)
     {
-        increment_func_index();
+        enum IndexCode index_code = increment_func_index();
+
+        if (index_code == Index_end)
+        {
+            loop_assign_active_funcs();
+        }
 
         accumulator = SDL_fmodf(accumulator, timesteplimit);