Fix error handling path in autovacuum launcher

The original code (since 00e6a16d01) was assuming aborting the
transaction in autovacuum launcher was sufficient to release all
resources, but in reality the launcher runs quite a lot of code out of
any transactions.  Re-introduce individual cleanup calls to make abort
more robust.

Reported-by: Robert Haas
Discussion: https://postgr.es/m/CA+TgmobQVbz4K_+RSmiM9HeRKpy3vS5xnbkL95gSEnWijzprKQ@mail.gmail.com

src/backend/postmaster/autovacuum.c

@@ -91,6 +91,7 @@
 #include "storage/proc.h"
 #include "storage/procsignal.h"
 #include "storage/sinvaladt.h"
+#include "storage/smgr.h"
 #include "tcop/tcopprot.h"
 #include "utils/dsa.h"
 #include "utils/fmgroids.h"
@@ -524,6 +525,26 @@ AutoVacLauncherMain(int argc, char *argv[])
 		/* Abort the current transaction in order to recover */
 		AbortCurrentTransaction();
 
+		/*
+		 * Release any other resources, for the case where we were not in a
+		 * transaction.
+		 */
+		LWLockReleaseAll();
+		pgstat_report_wait_end();
+		AbortBufferIO();
+		UnlockBuffers();
+		if (CurrentResourceOwner)
+		{
+			ResourceOwnerRelease(CurrentResourceOwner,
+								 RESOURCE_RELEASE_BEFORE_LOCKS,
+								 false, true);
+			/* we needn't bother with the other ResourceOwnerRelease phases */
+		}
+		AtEOXact_Buffers(false);
+		AtEOXact_SMgr();
+		AtEOXact_Files();
+		AtEOXact_HashTables(false);
+
 		/*
 		 * Now return to normal top-level context and clear ErrorContext for
 		 * next time.