Multiply RGB when reading image with unassociated alpha

src/tiff/tiffread.c

@@ -606,6 +606,12 @@ internal void read_strips(TiffReader *reader) {
         p->a = 255;
       } else {
         fread_with_offset(reader->fp, &(p->a), 1, alpha_offset);
+
+        if (alpha.type == ALPHA_TYPE_UNASSOCIATED) {
+          p->r *= p->a;
+          p->g *= p->a;
+          p->b *= p->a;
+        }
       }
 
       ++position;