fix: correct openedAt epoch corruption in PR merge MV (IN-1190) (#4320)

Signed-off-by: Gašper Grom <gasper.grom@gmail.com>

Author: gaspergrom

services/libs/tinybird/pipes/pull_request_analysis_baseline_merge_MV.pipe

@@ -254,7 +254,9 @@ SQL >
     SELECT
         if(existing.id != '', existing.id, new.id) as id,
         if(existing.sourceId != '', existing.sourceId, new.prSourceId) as sourceId,
-        COALESCE(existing.openedAt, new.openedAt) as openedAt,
+        if(
+            existing.openedAt != toDateTime(0), existing.openedAt, new.openedAt
+        ) as openedAt,
         if(existing.segmentId != '', existing.segmentId, new.segmentId) as segmentId,
         if(existing.channel != '', existing.channel, new.channel) as channel,
         if(existing.memberId != '', existing.memberId, new.memberId) as memberId,