[OpenJDK 2D-Dev] [9] Review Request: 4958064 JPGWriter does not throw UnsupportedException when canWriteSequence retuns false

[Sergey Bylokhov]

Hello.
Please review a small fix for jdk 9.
The API Doc for ImageWriter.PrepareWriteSequence() claims that this 
method will throw UnsupportedOperationException when canWriteSequence() 
returns false. But this does not seem to be happening for JPEG ImageWriter.
JPG writer has failed to override the method canWriteSequence() and 
relies on the parent class ImageWriter which returns a 'false' value by 
default.
But JPEGImageWriter class has actually implemented the method 
prepareWriteSequence() and it does not throw 
UnsupportedOperationException when canWriteSequence() returns false.

Bug: https://bugs.openjdk.java.net/browse/JDK-4958064
Webrev can be found at: 
http://cr.openjdk.java.net/~serb/4958064/webrev%2c01

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Best regards, Sergey.