Fix handling of 32-character SSID strings when scanning for access points on Esp8266

[mikee47]

This PR fixes a bug when scanning for access points on the Esp8266.

The code currently assumes that the SSID is NUL-terminated, but this cannot be relied upon.

I today started getting weird behaviour sending the network list over a websocket connection in JSON format.
If any of the JSON is malformed then the browser closes the connection.

The offending SSID was this:

44 49 52 45 43 54 2d 43 46 2d 48 50 20 44 65 73  DIRECT-CF-HP Des
6b 4a 65 74 20 32 39 30 30 20 73 65 72 69 65 73  kJet 2900 series
20 06 be                                          ..

The SSID buffer is only 32 characters long so the 20 06 be is junk which is not part of the name.
Clearly the ssid_len should have been used: we cannot assume SSID is NUL-terminated.