No check for SPIFFS size when writing to file

[UlliBien]

I'm using ARDUINO/ESP8266 Version 2.4.1. This system uses your SPIFFS implementation.

First I ask you to put a version number of the current version to "spiffs.h". This helps to check for actuality.

The major problem is, that there is no check for memory size. You can write more data into a file than free memory is available. This destroys the structure of SPIFFS. The only solution is reformatting the file system.