Error status of the last code conversion.
When an error was detected in the last code conversion, this variable
is set to one of the following symbols.
`insufficient-source'
`inconsistent-eol'
`invalid-source'
`interrupted'
`insufficient-memory'
When no error was detected, the value doesn't change. So, to check
the error status of a code conversion by this variable, you must
explicitly set this variable to nil before performing code
conversion.