Removing last network fails

[brainelectronics]

If only one network is configured, removing it will fail with the following report

* Running on http://192.168.4.1:80/
INFO:picoweb:699107456.207 <HTTPRequest object at 3f8425d0> <Stream object at 3f8423c0> "GET /favicon.ico"
INFO:picoweb:699107456.207 <HTTPRequest object at 3f844a70> <Stream object at 3f844860> "GET /configure"
DEBUG:WiFiManager:Existing config content: TP-LINK_FBFC3C
INFO:picoweb:699107456.207 <HTTPRequest object at 3f84c000> <Stream object at 3f84bb60> "GET /bootstrap.min.css"
DEBUG:WiFiManager:gzip accepted for CSS style file
DEBUG:WiFiManager:Accessed file static/css/bootstrap.min.css.gz
INFO:picoweb:699107456.207 <HTTPRequest object at 3f864dd0> <Stream object at 3f864bb0> "GET /favicon.ico"
INFO:picoweb:699107456.207 <HTTPRequest object at 3f869be0> <Stream object at 3f8699b0> "POST /remove_wifi_config"
INFO:WiFiManager:Remove networks: {'NETWORKNAME': 'NETWORKNAME'}
WARN:WiFiManager:Type: <class 'dict'>
DEBUG:WiFiManager:Read encrypted data: b'....'
DEBUG:WiFiManager:Decrypted data str: {'ssid': 'NETWORKNAME', 'password': 'NET_PW'}
DEBUG:WiFiManager:Decrypted data dict: {'ssid': 'NETWORKNAME', 'password': 'NET_PW'}
ERROR:picoweb:699107456.207 <HTTPRequest object at 3f869be0> <Stream object at 3f8699b0> TypeError('string indices must be integers, not str',)
Traceback (most recent call last):
  File "/lib/picoweb/__init__.py", line 206, in _handle
  File "/lib/wifi_manager/wifi_manager.py", line 719, in remove_wifi_config
  File "/lib/wifi_manager/wifi_manager.py", line 592, in _remove_wifi_config
TypeError: string indices must be integers, not str