Fix for rewriting uncompressed resources when exporting from solid WIM

Fix for rewriting uncompressed resources when exporting from solid WIM

The changes from commit 1ba2a3422b ("Workaround for WOF incompatibility")
are resulting in excessive, expensive decompressions when exporting small
incompressible files from solid blocks.  For now, add an optimization for
single chunk resources which prevents this common case from triggering
the degenerate behavior.