psql: Fix memory leak with repeated calls of \bind

Calling \bind repeatedly would cause the memory allocated for the list
of bind parameters to be leaked after each call, as the list is reset
when beginning a single call.

This issue is fixed by making the cleanup of the bind parameter list
more aggressive, refactoring it into a single routine called after
processing a query and before running an individual \bind.

HEAD required more surgery and has been fixed by 87eeadaea1.  Issue
introduced by 5b66de3433.

Reported-by: Anthonin Bonnefoy
Discussion: https://postgr.es/m/2e5b89af-a351-ff0a-000c-037ac28314ab@gmail.com
Backpatch-through: 16

src/bin/psql/command.c

@@ -470,7 +470,7 @@ exec_command_bind(PsqlScanState scan_state, bool active_branch)
 		int			nparams = 0;
 		int			nalloc = 0;
 
-		pset.bind_params = NULL;
+		clean_bind_state();
 
 		while ((opt = psql_scan_slash_option(scan_state, OT_NORMAL, NULL, false)))
 		{

src/bin/psql/common.c

@@ -1241,14 +1241,7 @@ sendquery_cleanup:
 	}
 
 	/* clean up after \bind */
-	if (pset.bind_flag)
-	{
-		for (i = 0; i < pset.bind_nparams; i++)
-			free(pset.bind_params[i]);
-		free(pset.bind_params);
-		pset.bind_params = NULL;
-		pset.bind_flag = false;
-	}
+	clean_bind_state();
 
 	/* reset \gset trigger */
 	if (pset.gset_prefix)
@@ -2413,6 +2406,26 @@ uri_prefix_length(const char *connstr)
 	return 0;
 }
 
+/*
+ * Reset state related to \bind
+ *
+ * Clean up any state related to bind parameters and bind_flag.  This needs
+ * to be called after processing a query or when running \bind.
+ */
+void
+clean_bind_state(void)
+{
+	if (pset.bind_flag)
+	{
+		for (int i = 0; i < pset.bind_nparams; i++)
+			free(pset.bind_params[i]);
+		free(pset.bind_params);
+	}
+
+	pset.bind_params = NULL;
+	pset.bind_flag = false;
+}
+
 /*
  * Recognized connection string either starts with a valid URI prefix or
  * contains a "=" in it.

src/bin/psql/common.h

@@ -41,6 +41,7 @@ extern bool standard_strings(void);
 extern const char *session_username(void);
 
 extern void expand_tilde(char **filename);
+extern void clean_bind_state(void);
 
 extern bool recognized_connection_string(const char *connstr);