PHRAS-270 #time 6h
nb: exiftool MUST be updated - issue opened
PHRAS-270 #time 3h
erase blank fields when writing metadatas = write back every field of the STRUCTURE, not only fields of the record.
Merge pull request #1155 from nlegoff/rebased-PHRAS-270

[3.8][PHRAS-270] Fix metadata rewriting