The constructors for PNGImageReaderSpi and PNGImageWriterSpi pass the
image metadata format names and native format name to their superclass
constructor in the paramater slots for 'streamMetadataFormatNames' and
'nativeStreamMetadataFormatName' in addition to the slots for the image
metadata names. Instead, these two parameters should be passed 'null'
values to indicate that stream metadata is not supported.

  A regression test will be placed in test/javax/imageio/PNGSpiStreamMetadata.java.