[FIX] runbot_merge: odd behaviour in try_closing

Could not reproduce it in a shell, but in the original version
`self.env.cr.rowcount` would always be 0 after the `modified`.

Turns out the check is really completely dumb, because if we got any
match in `select for update` we're going to find the same on in the
update, and thus the conditional is unnecessary. I've no idea why I
did that.

Anyway remove the conditional and just always try to unstage the PR.

runbot_merge/models/pull_requests.py

@@ -1358,23 +1358,21 @@ class PullRequests(models.Model):
         WHERE id = %s AND state != 'merged'
         FOR UPDATE SKIP LOCKED;
         ''', [self.id])
-        res = self.env.cr.fetchone()
-        if not res:
+        if not self.env.cr.fetchone():
             return False
 
         self.env.cr.execute('''
         UPDATE runbot_merge_pull_requests
         SET state = 'closed'
-        WHERE id = %s AND state != 'merged'
+        WHERE id = %s
         ''', [self.id])
         self.env.cr.commit()
         self.modified(['state'])
-        if self.env.cr.rowcount:
-            self.unstage(
-                "PR %s closed by %s",
-                self.display_name,
-                by
-            )
+        self.unstage(
+            "PR %s closed by %s",
+            self.display_name,
+            by
+        )
         return True
 
 # state changes on reviews