avfilter/vf_showpalette: Don't pretend disp_palette can fail

It can't fail, yet it returns an int and other code checks whether it
failed; yet if it did fail, an AVFrame would leak. One could of course
add an av_frame_free for this (that compilers could optimize away), yet
it is easier to simply stop pretending that disp_palette could fail.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

libavfilter/vf_showpalette.c

@@ -76,7 +76,7 @@ static int config_output(AVFilterLink *outlink)
     return 0;
 }
 
-static int disp_palette(AVFrame *out, const AVFrame *in, int size)
+static void disp_palette(AVFrame *out, const AVFrame *in, int size)
 {
     int x, y, i, j;
     uint32_t *dst = (uint32_t *)out->data[0];
@@ -88,12 +88,10 @@ static int disp_palette(AVFrame *out, const AVFrame *in, int size)
             for (j = 0; j < size; j++)
                 for (i = 0; i < size; i++)
                     dst[(y*dst_linesize + x) * size + j*dst_linesize + i] = pal[y*16 + x];
-    return 0;
 }
 
 static int filter_frame(AVFilterLink *inlink, AVFrame *in)
 {
-    int ret;
     AVFrame *out;
     AVFilterContext *ctx = inlink->dst;
     const ShowPaletteContext *s = ctx->priv;
@@ -105,9 +103,9 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *in)
         return AVERROR(ENOMEM);
     }
     av_frame_copy_props(out, in);
-    ret = disp_palette(out, in, s->size);
+    disp_palette(out, in, s->size);
     av_frame_free(&in);
-    return ret < 0 ? ret : ff_filter_frame(outlink, out);
+    return ff_filter_frame(outlink, out);
 }
 
 static const AVFilterPad showpalette_inputs[] = {