fix: postgresql GRANT user's permission after createDatabase, ensure database exist when GRANT

lib/private/Setup/PostgreSQL.php

@@ -40,7 +40,8 @@ class PostgreSQL extends AbstractDatabase {
 				} catch (DatabaseException $e) {
 					$canCreateRoles = false;
 				}
-
+				
+				$connectionMainDatabase;
 				if ($canCreateRoles) {
 					$connectionMainDatabase = $this->connect();
 					//use the admin login data for the new database user
@@ -51,16 +52,6 @@ class PostgreSQL extends AbstractDatabase {
 					$this->dbPassword = \OC::$server->get(ISecureRandom::class)->generate(30, ISecureRandom::CHAR_ALPHANUMERIC);
 
 					$this->createDBUser($connection);
-
-					// Go to the main database and grant create on the public schema
-					// The code below is implemented to make installing possible with PostgreSQL version 15:
-					// https://www.postgresql.org/docs/release/15.0/
-					// From the release notes: For new databases having no need to defend against insider threats, granting CREATE permission will yield the behavior of prior releases
-					// Therefore we assume that the database is only used by one user/service which is Nextcloud
-					// Additional services should get installed in a separate database in order to stay secure
-					// Also see https://www.postgresql.org/docs/15/ddl-schemas.html#DDL-SCHEMAS-PATTERNS
-					$connectionMainDatabase->executeQuery('GRANT CREATE ON SCHEMA public TO "' . addslashes($this->dbUser) . '"');
-					$connectionMainDatabase->close();
 				}
 			}
 
@@ -73,6 +64,18 @@ class PostgreSQL extends AbstractDatabase {
 			$this->createDatabase($connection);
 			// the connection to dbname=postgres is not needed anymore
 			$connection->close();
+
+			if ($canCreateRoles) {
+				// Go to the main database and grant create on the public schema
+				// The code below is implemented to make installing possible with PostgreSQL version 15:
+				// https://www.postgresql.org/docs/release/15.0/
+				// From the release notes: For new databases having no need to defend against insider threats, granting CREATE permission will yield the behavior of prior releases
+				// Therefore we assume that the database is only used by one user/service which is Nextcloud
+				// Additional services should get installed in a separate database in order to stay secure
+				// Also see https://www.postgresql.org/docs/15/ddl-schemas.html#DDL-SCHEMAS-PATTERNS
+				$connectionMainDatabase->executeQuery('GRANT CREATE ON SCHEMA public TO "' . addslashes($this->dbUser) . '"');
+				$connectionMainDatabase->close();
+			}
 		} catch (\Exception $e) {
 			$this->logger->warning('Error trying to connect as "postgres", assuming database is setup and tables need to be created', [
 				'exception' => $e,