SD-Lib: File-Class missing destrutor

[agdl]

From @basti2k on May 4, 2016 14:20

In the File-Class of the SD-Library would been allocated memory with "malloc", but the Class hasn't a destructor to release the allocated memory.

Copied from original issue: arduino/Arduino#4922

[cmaglie]

@basti2k
the malloc-ed resource is freed inside the close() method:

SD/src/File.cpp

Lines 127 to 131 in f4f3b0c

	void File::close() {
	if (_file) {
	_file->close();
	free(_file);
	_file = 0;

Placing another free inside an object destructor may cause other issue if the object is copied.