Make init() return sensible error code rather than -1 in case of

invalid values.

Originally committed as revision 25248 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavfilter/vf_scale.c

@@ -58,7 +58,7 @@ static av_cold int init(AVFilterContext *ctx, const char *args, void *opaque)
     /* sanity check params */
     if (scale->w <  -1 || scale->h <  -1) {
         av_log(ctx, AV_LOG_ERROR, "Size values less than -1 are not acceptable.\n");
-        return -1;
+        return AVERROR(EINVAL);
     }
     if (scale->w == -1 && scale->h == -1)
         scale->w = scale->h = 0;