Fix for Bug #35970: Freestyle + Particles = Crash.

The crash was caused by a reference of freed memory in add_halo_flare() that relied
on the global variable R to retrieve a list of objects.  The value of this variable
is invalidated by a nested execution of the Blender Internal renderer for Freestyle
stroke rendering, leading to the documented memory reference issue.

source/blender/render/intern/source/pipeline.c

@@ -1676,6 +1676,9 @@ static void add_freestyle(Render *re, int render)
 	}
 
 	FRS_finish_stroke_rendering(re);
+
+	/* restore the global R value (invalidated by nested execution of the internal renderer) */
+	R = *re;
 }
 
 /* merges the results of Freestyle stroke rendering into a given render result */