fdo#77454: fix WW8 import/export of negative image crop

The negative crop values were imported as large positive values, which
caused the image to be rendered with 1 pixel width after commit
2e5167528f7566dd9b000e50fc1610b7bf99132a.

Change-Id: I0e01b9d9a05d90e868699832085a06ba5aab7e54
SvxMSDffImportRec: these members are all 32bit "signed integers"

Change-Id: Iee1dab4895970628e5f5c4ee6070f7f67ba2df8c