Better writer tests.

Fixed a bug in PICTWriter.
Minor changes in ImageReader/WriterBase classes.

imageio/imageio-core/src/main/java/com/twelvemonkeys/imageio/ImageReaderBase.java

@@ -99,9 +99,13 @@ public abstract class ImageReaderBase extends ImageReader {
     public void setInput(final Object input, final boolean seekForwardOnly, final boolean ignoreMetadata) {
         resetMembers();
         super.setInput(input, seekForwardOnly, ignoreMetadata);
+
         if (input instanceof ImageInputStream) {
             imageInput = (ImageInputStream) input;
         }
+        else {
+            imageInput = null;
+        }
     }
 
     @Override

imageio/imageio-core/src/main/java/com/twelvemonkeys/imageio/ImageWriterBase.java

@@ -83,6 +83,9 @@ public abstract class ImageWriterBase extends ImageWriter {
         if (output instanceof ImageOutputStream) {
             imageOutput = (ImageOutputStream) output;
         }
+        else {
+            imageOutput = null;
+        }
     }
 
     /**