IO errors are not handled when UseFolder points to non-existing directory

[thmshmm]

When UseFolder is set to a non-existing directory

go-approval-tests/approvals.go

Line 78 in 434b910

err := namer.compare(namer.getApprovalFile(extWithDot), namer.getReceivedFile(extWithDot), reader)

just received does not match approved is logged instead of the actual no such file or directory
error that was generated in dumpReceivedTestResult.