Treat empty SSH settings in the config as not set

The example config has empty remote_sudo and numeric_ids values, which
made getboolean fail with "Bad configuration file" if the [server]
section was uncommented, and an empty ssh_keyfile was used as the key
path. Treat empty values as false or not set, and show false in the
example config.

simple_backup/simple_backup.conf

@@ -18,5 +18,5 @@ keep=-1
 # ssh_host=
 # ssh_user=
 # ssh_keyfile=
-# remote_sudo=
-# numeric_ids=
+# remote_sudo=false
+# numeric_ids=false

simple_backup/simple_backup.py

@@ -849,26 +849,14 @@ def _read_config(config_file, user: Optional[str] = None):
     config_args['ssh_host'] = config.get('server', 'ssh_host', fallback='').strip() or None
     config_args['ssh_user'] = config.get('server', 'ssh_user', fallback='').strip() or None
 
-    try:
-        ssh_keyfile = config.get('server', 'ssh_keyfile')
-    except (configparser.NoSectionError, configparser.NoOptionError):
-        ssh_keyfile = None
+    config_args['ssh_keyfile'] = config.get('server', 'ssh_keyfile', fallback='').strip() or None
 
-    config_args['ssh_keyfile'] = ssh_keyfile
-
-    try:
-        remote_sudo = config.getboolean('server', 'remote_sudo')
-    except (configparser.NoSectionError, configparser.NoOptionError):
-        remote_sudo = False
-
-    config_args['remote_sudo'] = remote_sudo
-
-    try:
-        numeric_ids = config.getboolean('server', 'numeric_ids')
-    except (configparser.NoSectionError, configparser.NoOptionError):
-        numeric_ids = False
-
-    config_args['numeric_ids'] = numeric_ids
+    # Empty values (as in the example config) count as false
+    for key in ['remote_sudo', 'numeric_ids']:
+        if config.get('server', key, fallback='').strip() == '':
+            config_args[key] = False
+        else:
+            config_args[key] = config.getboolean('server', key)
 
     return config_args