Raid re-anchor: only treat POPULATED unanchored headers as a change

Review follow-up (PR #212). The headerUnanchored probe flagged any shown
group header with no resolved rect, but the secure position snippet
legitimately leaves EMPTY visible groups unanchored — so in any raid that
doesn't fill all enabled groups the probe fired every pass, permanently
defeating the redundant-reposition early-out and reintroducing snap jitter.
Gate on counts[gi] > 0 (already computed in the same block): the real bug
has populated-but-unanchored headers, so it is still caught.

Author: Krathe82

Frames/Headers.lua

@@ -3783,19 +3783,23 @@ function DF:ApplyRaidGroupSorting()
             end
         end
 
-        -- A header can be shown yet UNANCHORED: the secure position snippet
-        -- ClearAllPoints()s every group header and only re-anchors populated
-        -- slots, so a raid-to-party collapse (all counts hit 0) strips the
-        -- anchors while the caches above still describe the populated raid.
-        -- Converting back with the same roster, nothing above reads as
-        -- changed, and the early-out below would skip the only reposition
-        -- that could re-anchor the headers — frames stay alive (shown,
-        -- units assigned, alpha 1) but draw nothing until a /reload.
-        -- GetLeft() is nil on a frame with no resolved rect.
+        -- A POPULATED header can be shown yet UNANCHORED: the secure position
+        -- snippet ClearAllPoints()s every group header and only re-anchors
+        -- populated slots, so a raid-to-party collapse (all counts hit 0)
+        -- strips the anchors while the caches above still describe the
+        -- populated raid. Converting back with the same roster, nothing above
+        -- reads as changed, and the early-out below would skip the only
+        -- reposition that could re-anchor the headers — frames stay alive
+        -- (shown, units assigned, alpha 1) but draw nothing until a /reload.
+        -- GetLeft() is nil on a frame with no resolved rect. Gate on
+        -- counts[gi] > 0: an EMPTY visible group is legitimately left
+        -- unanchored by the same snippet, so testing it would fire on every
+        -- pass in any raid that doesn't fill all enabled groups, permanently
+        -- defeating the redundant-reposition early-out.
         local headerUnanchored = false
         for gi = 1, 8 do
             local gh = DF.raidSeparatedHeaders[gi]
-            if gh and gh:IsShown() and not gh:GetLeft() then
+            if gh and counts[gi] > 0 and gh:IsShown() and not gh:GetLeft() then
                 headerUnanchored = true
                 break
             end