avfilter/vf_alphamerge: do not check for ret value if all wanted frames are present

It is not needed and may be uninitialized.

libavfilter/vf_alphamerge.c

@@ -154,14 +154,12 @@ static int activate(AVFilterContext *ctx)
     }
 
     if (s->main_frame && s->alpha_frame) {
-        if (ret > 0) {
         draw_frame(ctx, s->main_frame, s->alpha_frame);
         ret = ff_filter_frame(outlink, s->main_frame);
         av_frame_free(&s->alpha_frame);
         s->main_frame = NULL;
         return ret;
     }
-    }
 
     FF_FILTER_FORWARD_STATUS(ctx->inputs[0], outlink);
     FF_FILTER_FORWARD_STATUS(ctx->inputs[1], outlink);