WMF: Improved error reporting.
WMF: Improved error reporting.

When loading the source fails because the file format is not supported, we
now report a FormatError instead of a ResourceError.
When the file format is supported but the media cannot be played (topology
cannot be resolved), it is most likely caused by a missing codec and we
then report a FormatError.

Change-Id: I101a86c129a0c5dccb543fc1247cb741994684fd
Reviewed-by: Andy Nichols <3d1e63b963f99f97839545621c6a9a8e2b2ab8fd@digia.com>

mer-qt/qtmultimedia,webOS-ports/qtmultimedia,nezticle/qtmultimedia,webOS-ports/qtmultimedia,mer-qt/qtmultimedia,jfaust/qtmultimedia,sergiusens/qtmultimedia,mer-qt/qtmultimedia,nezticle/qtmultimedia,nezticle/qtmultimedia,jfaust/qtmultimedia,nezticle/qtmultimedia,jfaust/qtmultimedia,webOS-ports/qtmultimedia,webOS-ports/qtmultimedia,sergiusens/qtmultimedia,nezticle/qtmultimedia,sergiusens/qtmultimedia,sergiusens/qtmultimedia,mer-qt/qtmultimedia,jfaust/qtmultimedia,jfaust/qtmultimedia,mer-qt/qtmultimedia,webOS-ports/qtmultimedia,sergiusens/qtmultimedia