Silence compiler warning.

Assorted buildfarm members are complaining about "'process_list' may
be used uninitialized in this function" since f76892c9f, presumably
because they don't trust that the switch case labels are exhaustive.
We can silence that by initializing the variable to NULL.  Should
a switch fall-through actually happen, we'll get SIGSEGV at the
first use, which is as good as an Assert.

src/bin/scripts/reindexdb.c

@@ -286,7 +286,7 @@ reindex_one_database(ConnParams *cparams, ReindexType type,
 	SimpleStringListCell *cell;
 	SimpleOidListCell *indices_tables_cell = NULL;
 	bool		parallel = concurrentCons > 1;
-	SimpleStringList *process_list;
+	SimpleStringList *process_list = NULL;
 	SimpleOidList *tableoid_list = NULL;
 	ReindexType process_type = type;
 	ParallelSlotArray *sa;