Fix integer truncation in OpenFileByIndex due to change in sdfat library

[wolfmanjm]

[watbulb]

This pull request doesn't seem to make a lot of sense: oflag_t is a typedef to int/uint8_t within FatApiConstants.h

Am I missing something @wolfmanjm ? Can you provide an example of the truncation behavior? If somehow this is the case it would require also including <fcntl.h> as far as I can tell.

[wolfmanjm]

o_flag_t is not a uint_t in certain cases (https://github.com/greiman/SdFat/blob/master/src/FatLib/FatApiConstants.h#L29) if USE_FCNTL_H is not defined it is 32bits. In the case of a newlib system it is 32 bits not 8 bits, and if coded to 8 bits will truncate the flag from the 32 bit definition to 8 bits causing it to not work as expected. Using this typedef fixes the issue in all cases. The issue was noted here and I ran into the same issue. https://forum.pjrc.com/threads/43050-MTP-Responder-Contribution?p=199532&viewfull=1#post199532

[ghost]

Hi guys, I wasn't able to copy a new file in the mounted SD (the file seems copied but size was 0)... after applying this fix it works fine. Hope it will be merged on master.

Thanks!

[xenington]

This patch is necessary for MTP to work in Ubuntu 18.04.

Thank you Wolfmanjm.