Make Display, Pbuffer and AWTGLCanvas fail on null PixelFormats

src/java/org/lwjgl/opengl/AWTGLCanvas.java

@@ -147,6 +147,8 @@ public class AWTGLCanvas extends Canvas implements Drawable, ComponentListener,
 	 */
 	public AWTGLCanvas(GraphicsDevice device, PixelFormat pixel_format, Drawable drawable) throws LWJGLException {
 		super(implementation.findConfiguration(device, pixel_format));
+		if (pixel_format == null)
+			throw new NullPointerException("Pixel format must be non-null");
 		addHierarchyListener(this);
 		this.drawable = drawable;
 		this.pixel_format = pixel_format;

src/java/org/lwjgl/opengl/Display.java

@@ -646,6 +646,8 @@ public final class Display {
 	 * @throws LWJGLException
 	 */
 	public static void create(PixelFormat pixel_format, Drawable shared_drawable) throws LWJGLException {
+		if (pixel_format == null)
+			throw new NullPointerException("Pixel format must be non-null");
 		if (isCreated())
 			throw new IllegalStateException("Only one LWJGL context may be instantiated at any one time.");
 		if (pixel_format == null)

src/java/org/lwjgl/opengl/Pbuffer.java

@@ -178,6 +178,8 @@ public final class Pbuffer implements Drawable {
 	 * 						 with the Display context (if created).
 	 */
 	public Pbuffer(int width, int height, PixelFormat pixel_format, RenderTexture renderTexture, Drawable shared_drawable) throws LWJGLException {
+		if (pixel_format == null)
+			throw new NullPointerException("Pixel format must be non-null");
 		this.width = width;
 		this.height = height;
 		this.peer_info = createPbuffer(width, height, pixel_format, renderTexture);