ReaderInputStream discards some encoding errors

Description

org.apache.commons.io.input.ReaderInputStream discards encoder errors in some cases instead of properly rethrowing them.

The underlying issue is that lastCoderResult is re-assigned before it has been checked for errors and overflow (link to code).

This was originally mentioned in pull request #293.

Example

The read() call in the following example should throw an exception, but currently it erroneously returns -1.

// Encoder which throws on malformed or unmappable input
CharsetEncoder encoder = StandardCharsets.UTF_8.newEncoder();
ReaderInputStream in = new ReaderInputStream(new StringReader("\uD800"), encoder);
// BUG: This should have thrown an exception because the input is malformed
System.out.println("Read: " + in.read());