Clarify java.io.Reader.read(char[], ...) behavior for full array

Summary

Add verbiage making explicit the behavior of the Reader methods read(char[] cbuf) when cbuf.length is zero and read(char[] cbuf, int off, int len) when len is zero.

Problem

The behaviors of read(char[] cbuf) when cbuf.length is zero and read(char[] cbuf, int off, int len) when len is zero are not as completely specified as in the analogous InputStream methods.

Solution

Add verbiage making explicit the behavior of the Reader methods read(char[] cbuf) when cbuf.length is zero and read(char[] cbuf, int off, int len) when len is zero.

Specification

To the specification of Reader::read(char[]) add the paragraph

If the length of cbuf is zero, then no characters are read and 0 is returned; otherwise, there is an attempt to read at least one character. If no character is available because the stream is at its end, the value -1 is returned; otherwise, at least one character is read and stored into cbuf.

and to that of Reader::read(char[],int,int) add the paragraph

If len is zero, then no characters are read and 0 is returned; otherwise, there is an attempt to read at least one character. If no character is available because the stream is at its end, the value -1 is returned; otherwise, at least one character is read and stored into cbuf.