Calloc function tries to allocate 4096 bytes.
If such memory is not available, it returns NULL pointer.
This exception was not handled in the code, causing a dirty crash.
A 0 length string is still a valid input and should be treated as such, a NULL return should be reserved for when errors occur during line editing or EOF is reached.
Merges https://github.com/espressif/esp-idf/pull/4926
