Fix: Smoke wasn't using pointcache properly.

* The cache was reset almost constantly because smoke didn't save the first frame into cache. Although not necessary for smoke, it's vital to pointcache.
* Added info message to smoke cache panel for non saved files.
* Now smoke also only updates with a framestep of 1, so that scrubbing the timeline doesn't mess up the simulation.
* Among other things fixes report #23731.

release/scripts/ui/properties_physics_common.py

@@ -51,6 +51,11 @@ def point_cache_ui(self, context, cache, enabled, cachetype):
 
         layout.label(text=cache.info)
     else:
+        if cachetype == 'SMOKE':
+            if bpy.data.is_dirty:
+                layout.label(text="Cache is disabled until the file is saved")
+                layout.enabled = false
+
         layout.prop(cache, "name", text="File Name")
 
         split = layout.split()