libsparse: Propagate failures when resparsing files.

MappedFile creation can fail due to out of memory, but this condition is
not handled properly when resparsing. The error is silently ignored and
the result is a corrupt file.

Bug: 273933042
Bug: 268872725
Test: fastboot update on Windows
Change-Id: I4d0f24d6ba390e2328de8f0e3637d17663743df5