Reset InstallXLogFileSegmentActive after walreceiver self-initiated exit.

After commit cc2c7d65fc added this flag,
failure to reset it caused assertion failures.  In non-assert builds, it
made the system fail to achieve the objectives listed in that commit;
chiefly, we might emit a spurious log message.  Back-patch to v15, where
that commit first appeared.

Bharath Rupireddy and Kyotaro Horiguchi.  Reviewed by Dilip Kumar,
Nathan Bossart and Michael Paquier.  Reported by Dilip Kumar.

Discussion: https://postgr.es/m/CAFiTN-sE3ry=ycMPVtC+Djw4Fd7gbUGVv_qqw6qfzp=JLvqT3g@mail.gmail.com

src/backend/access/transam/xlogrecovery.c

@@ -3535,8 +3535,7 @@ WaitForWALToBecomeAvailable(XLogRecPtr RecPtr, bool randAccess,
 					 * walreceiver is not active, so that it won't overwrite
 					 * WAL that we restore from archive.
 					 */
-					if (WalRcvStreaming())
-						XLogShutdownWalRcv();
+					XLogShutdownWalRcv();
 
 					/*
 					 * Before we sleep, re-scan for possible new timelines if