Fix compiler warning in pg_logicalinspect.

Oversight in bd65cb3cd4.

Reported-by: David Rowley <dgrowleyml@gmail.com>
Reported-by: Nathan Bossart <nathandbossart@gmail.com>
Author: David Rowley <dgrowleyml@gmail.com>
Discussion: https://postgr.es/m/CAApHDvqrhFfnetbcwgGkJ=z63T8HfQ_OyP=vX8BYiXyxFKt67w@mail.gmail.com

contrib/pg_logicalinspect/pg_logicalinspect.c

@@ -85,6 +85,8 @@ parse_snapshot_filename(const char *filename)
 parse_error:
 	ereport(ERROR,
 			errmsg("invalid snapshot file name \"%s\"", filename));
+
+	return InvalidXLogRecPtr;					/* keep compiler quiet */
 }
 
 /*