fix: calling imlib2 with color modifier being NULL (#440)

the multiframe loaders sets the color modifier to NULL but doesn't
restore it before returning. this results in a imlib2 developer warning
if you try to change brightness/contrast on a multiframe image (which
doesn't have alpha).

ensure that the color modifier is restored before returning under all
paths.

Reported-by: Madhu

Reviewed-on: https://codeberg.org/nsxiv/nsxiv/pulls/440
Reviewed-by: eylles <eylles@noreply.codeberg.org>

image.c

@@ -470,11 +470,6 @@ static bool img_load_multiframe(img_t *img, const fileinfo_t *file)
 		m->frames = erealloc(m->frames, m->cap * sizeof(*m->frames));
 	}
 
-	imlib_context_set_dither(0);
-	imlib_context_set_anti_alias(0);
-	imlib_context_set_color_modifier(NULL);
-	imlib_context_set_operation(IMLIB_OP_COPY);
-
 	if ((blank = imlib_create_image(img->w, img->h)) == NULL) {
 		error(0, 0, "%s: couldn't create image", file->name);
 		return false;
@@ -482,6 +477,11 @@ static bool img_load_multiframe(img_t *img, const fileinfo_t *file)
 	imlib_context_set_image(blank);
 	img_area_clear(0, 0, img->w, img->h);
 
+	imlib_context_set_dither(0);
+	imlib_context_set_anti_alias(0);
+	imlib_context_set_color_modifier(NULL);
+	imlib_context_set_operation(IMLIB_OP_COPY);
+
 	/*
 	 * Imlib2 gives back a "raw frame", we need to blend it on top of the
 	 * previous frame ourselves if necessary to get the fully decoded frame.
@@ -548,6 +548,7 @@ static bool img_load_multiframe(img_t *img, const fileinfo_t *file)
 	imlib_context_set_image(blank);
 	imlib_free_image();
 	img_multiframe_context_set(img);
+	imlib_context_set_color_modifier(img->cmod); /* restore cmod */
 	return m->cnt > 0;
 }
 #endif /* HAVE_IMLIB2_MULTI_FRAME */