framebuffer: Checks if glBindFramebuffer() exists when using GLES1

With GLES 1, frame buffers are a optional extensions. We need to make
sure the pointer exist before calling the function and do that by just
checkout the corresponding feature.

cogl/cogl-framebuffer.c

@@ -1373,6 +1373,8 @@ bind_gl_framebuffer (CoglContext *ctx,
         _cogl_framebuffer_get_winsys (framebuffer);
       winsys->onscreen_bind (COGL_ONSCREEN (framebuffer));
 #endif
+      /* glBindFramebuffer is an an extension with OpenGL ES 1.1 */
+      if (cogl_features_available (COGL_FEATURE_OFFSCREEN))
         GE (glBindFramebuffer (target, 0));
     }
 }