avfilter/lavfutils: use image2pipe demuxer on ff_load_image

allow protocols other than file to be used
for example, use data protocol to embed a file in script

Signed-off-by: Muhammad Faiz <mfcc64@gmail.com>

libavfilter/lavfutils.c

@@ -38,7 +38,7 @@ int ff_load_image(uint8_t *data[4], int linesize[4],
 
     av_register_all();
 
-    iformat = av_find_input_format("image2");
+    iformat = av_find_input_format("image2pipe");
     if ((ret = avformat_open_input(&format_ctx, filename, iformat, NULL)) < 0) {
         av_log(log_ctx, AV_LOG_ERROR,
                "Failed to open input file '%s'\n", filename);