Fix demo desyncs caused by P_RunThinkers() change.

1bcff874c52a changed the behavior of P_RunThinkers() to avoid
dereferencing thinker pointers after they had been freed, but the
modified version of the function was not logically equivalent to
Vanilla version, because the 'next' pointer can be changed by the
thinker function if one is invoked.

This fixes a desync in tnt-speed-movie-0443131.lmp. Thanks to Zvonimir
Bužanić for the bug report and Fabian Greffrath for reporting.

Fixes #547.

1 files changed, 5 insertions, 4 deletions

diff --git a/src/hexen/p_tick.c b/src/hexen/p_tick.c
index c58d6e82..3d3dd389 100644
--- a/src/hexen/p_tick.c
+++ b/src/hexen/p_tick.c
@@ -91,17 +91,18 @@ static void RunThinkers(void)
     currentthinker = thinkercap.next;
     while (currentthinker != &thinkercap)
     {
-        nextthinker = currentthinker->next;
-
         if (currentthinker->function == (think_t) - 1)
         {                       // Time to remove it
+            nextthinker = currentthinker->next;
             currentthinker->next->prev = currentthinker->prev;
             currentthinker->prev->next = currentthinker->next;
             Z_Free(currentthinker);
         }
-        else if (currentthinker->function)
+        else
         {
-            currentthinker->function(currentthinker);
+            if (currentthinker->function)
+                currentthinker->function(currentthinker);
+            nextthinker = currentthinker->next;
         }
 
         currentthinker = nextthinker;