checkGLError in LwjglOffscreenBuffer is now called only if assertions are on, as it is done in LwjglAbstractDisplay

jme3-lwjgl/src/main/java/com/jme3/system/lwjgl/LwjglOffscreenBuffer.java

@@ -123,7 +123,7 @@ public class LwjglOffscreenBuffer extends LwjglContext implements Runnable {
         }
 
         listener.update();
-        checkGLError();
+        assert checkGLError();
 
         renderer.postFrame();