Add LIBMTP_Get_Thumbnail_Format to get thumbnail format of a file.

src/libmtp.h

Index: src/libmtp.h
diff --git a/src/libmtp.h b/src/libmtp.h
index f923cc1239b50c496e74bfe7c807353194eb5799..07aa27394b7e1f3212fd3dc536ad786cc22b76c6 100644
--- a/src/libmtp.h
+++ b/src/libmtp.h
@@ -924,6 +924,8 @@ int LIBMTP_Get_Representative_Sample(LIBMTP_mtpdevice_t *, uint32_t const,
                           LIBMTP_filesampledata_t *);
 int LIBMTP_Get_Thumbnail(LIBMTP_mtpdevice_t *, uint32_t const,
                          unsigned char **data, unsigned int *size);
+int LIBMTP_Get_Thumbnail_Format(LIBMTP_mtpdevice_t *device, uint32_t const id,
+                                uint16_t *format);
 
 /**
  * @}