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, 2 insertions, 2 deletions

diff --git a/src/doom/p_tick.c b/src/doom/p_tick.c
index c933cfe9..5a93b80f 100644
--- a/src/doom/p_tick.c
+++ b/src/doom/p_tick.c
@@ -98,11 +98,10 @@ void P_RunThinkers (void)
     currentthinker = thinkercap.next;
     while (currentthinker != &thinkercap)
     {
-        nextthinker = currentthinker->next;
-
 	if ( currentthinker->function.acv == (actionf_v)(-1) )
 	{
 	    // time to remove it
+            nextthinker = currentthinker->next;
 	    currentthinker->next->prev = currentthinker->prev;
 	    currentthinker->prev->next = currentthinker->next;
 	    Z_Free(currentthinker);
@@ -111,6 +110,7 @@ void P_RunThinkers (void)
 	{
 	    if (currentthinker->function.acp1)
 		currentthinker->function.acp1 (currentthinker);
+            nextthinker = currentthinker->next;
 	}
 	currentthinker = nextthinker;
     }