When multiple image child elements are inside a frame, each one is
imported and gets unique name via SwDoc::SetFlyName(). But the
retained one is not necessarily the first one, which is the only one
that may have the original name.
Also the solveMultipleImages needs to return a smart pointer, as nothing
else keeps the image contexts alive.
(regression from 44cfc7cb6533d827fd2d6e586d92c61d7d7f7a70)
Change-Id: I28a8a752f3eed176cc2ebb4c9af11a0dd4d18ea6
b69d152cfa