perf scripts python: export-to-postgresql.py: Fix invalid input syntax for integer error

Fix SQL query error "invalid input syntax for integer":

  Traceback (most recent call last):
    File "tools/perf/scripts/python/export-to-postgresql.py", line 465, in <module>
      do_query(query, 'CREATE VIEW calls_view AS '
    File "tools/perf/scripts/python/export-to-postgresql.py", line 274, in do_query
      raise Exception("Query failed: " + q.lastError().text())
  Exception: Query failed: ERROR:  invalid input syntax for integer: ""
  LINE 1: ...ch_count,call_id,return_id,CASE WHEN flags=0 THEN '' WHEN fl...
                                                               ^
  (22P02) QPSQL: Unable to create query
  Error running python script tools/perf/scripts/python/export-to-postgresql.py

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Fixes: f08046cb30 ("perf thread-stack: Represent jmps to the start of a different symbol")
Link: https://lkml.kernel.org/n/tip-strfpdozrvg7bi1xzrivxzqt@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/scripts/python/export-to-postgresql.py

@@ -478,7 +478,7 @@ if perf_db_export_calls:
 			'branch_count,'
 			'call_id,'
 			'return_id,'
-			'CASE WHEN flags=0 THEN \'\' WHEN flags=1 THEN \'no call\' WHEN flags=2 THEN \'no return\' WHEN flags=3 THEN \'no call/return\' WHEN flags=6 THEN \'jump\' ELSE flags END AS flags,'
+			'CASE WHEN flags=0 THEN \'\' WHEN flags=1 THEN \'no call\' WHEN flags=2 THEN \'no return\' WHEN flags=3 THEN \'no call/return\' WHEN flags=6 THEN \'jump\' ELSE CAST ( flags AS VARCHAR(6) ) END AS flags,'
 			'parent_call_path_id'
 		' FROM calls INNER JOIN call_paths ON call_paths.id = call_path_id')