Sort the export formats

So that they are ordered the same on all platforms.

src/file_format.c

@@ -34,10 +34,18 @@ static bool endswith(const char *str, const char *end)
     return strcmp(start, end) == 0;
 }
 
+static int file_format_cmp(const file_format_t *a, const file_format_t *b)
+{
+    if (b->priority != a->priority) {
+        return b->priority - a->priority;
+    }
+    return strcmp(a->name, b->name);
+}
 
 void file_format_register(file_format_t *format)
 {
     DL_APPEND(file_formats, format);
+    DL_SORT(file_formats, file_format_cmp);
 }
 
 const file_format_t *file_format_get(

src/file_format.h

@@ -34,6 +34,7 @@ struct file_format
     int             (*import_func)(const file_format_t *format, image_t *img,
                                    const char *path);
     void            (*import_gui)(file_format_t *format);
+    int             priority; // Specifies the order of file_format_iter.
 };
 
 void file_format_register(file_format_t *format);

src/formats/gltf.c

@@ -456,4 +456,5 @@ FILE_FORMAT_REGISTER(gltf,
     .exts_desc = "glTF2",
     .export_gui = export_gui,
     .export_func = export_as_gltf,
+    .priority = 100,
 )

src/formats/png.c

@@ -79,4 +79,5 @@ FILE_FORMAT_REGISTER(png,
     .exts_desc = "png",
     .export_gui = export_gui,
     .export_func = export_as_png,
+    .priority = 90,
 )