Check clipboard contents for safety.

Problems can occur within these helper functions as the polling is extremely quick, causing for an edge case where the user copies content before the clipboard has time to process the contents

src/main/java/me/goudham/ClipboardListener.java

@@ -49,7 +49,9 @@ abstract class ClipboardListener {
         BufferedImage bufferedImage = null;
 
         try {
+            if (clipboardContents.isDataFlavorSupported(IMAGE.getDataFlavor())) {
                 bufferedImage = ClipboardUtils.convertToBufferedImage((Image) clipboardContents.getTransferData(IMAGE.getDataFlavor()));
+            }
         } catch (UnsupportedFlavorException | IOException exp) {
             exp.printStackTrace();
         }