patch 8.0.1657: crash when reading a channel

Problem:    Crash when reading a channel.
Solution:   Clear the write flag before writing. (idea by Shinya Ohyanagi,
            closes #2769).

src/version.c

@@ -762,6 +762,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1657,
 /**/
     1656,
 /**/