avfilter/vf_curves: unmap the psfile with the mapped pointer and size

parse_psfile() advances buf and decrements size while reading the
file, and then passed these to av_file_unmap() instead of what
av_file_map() returned. With mmap, munmap() then fails with EINVAL
because the pointer is no longer page aligned, so the mapping leaks on
every init and every psfile command; on builds without mmap, av_free()
is called on a pointer into the middle of the buffer.

Keep the mapped pointer and size and unmap those.

Signed-off-by: Martin Mirchev <mmirchev@comp.nus.edu.sg>

libavfilter/vf_curves.c

@@ -586,17 +586,19 @@ end:
 static int parse_psfile(AVFilterContext *ctx, const char *fname)
 {
     CurvesContext *curves = ctx->priv;
-    uint8_t *buf;
-    size_t size;
+    uint8_t *map, *buf;
+    size_t map_size, size;
     int i, ret, version av_unused, nb_curves;
     AVBPrint ptstr;
     static const int comp_ids[] = {3, 0, 1, 2};
 
     av_bprint_init(&ptstr, 0, AV_BPRINT_SIZE_AUTOMATIC);
 
-    ret = av_file_map(fname, &buf, &size, 0, NULL);
+    ret = av_file_map(fname, &map, &map_size, 0, NULL);
     if (ret < 0)
         return ret;
+    buf  = map;
+    size = map_size;
 
 #define READ16(dst) do {                \
     if (size < 2) {                     \
@@ -635,7 +637,7 @@ static int parse_psfile(AVFilterContext *ctx, const char *fname)
     }
 end:
     av_bprint_finalize(&ptstr, NULL);
-    av_file_unmap(buf, size);
+    av_file_unmap(map, map_size);
     return ret;
 }