patch 8.0.0988: warning from Covscan about using NULL pointer

Problem:    Warning from Covscan about using NULL pointer.
Solution:   Add extra check for NULL. (zdohnal)

Author: brammool

src/fileio.c

@@ -1370,7 +1370,8 @@ readfile(
 		 * Decrypt the read bytes.  This is done before checking for
 		 * EOF because the crypt layer may be buffering.
 		 */
-		if (cryptkey != NULL && size > 0)
+		if (cryptkey != NULL && curbuf->b_cryptstate != NULL
+								   && size > 0)
 		{
 		    if (crypt_works_inplace(curbuf->b_cryptstate))
 		    {

src/undo.c

@@ -921,7 +921,7 @@ undo_write(bufinfo_T *bi, char_u *ptr, size_t len)
     static int
 undo_flush(bufinfo_T *bi)
 {
-    if (bi->bi_buffer != NULL && bi->bi_used > 0)
+    if (bi->bi_buffer != NULL && bi->bi_state != NULL && bi->bi_used > 0)
     {
 	crypt_encode_inplace(bi->bi_state, bi->bi_buffer, bi->bi_used);
 	if (fwrite(bi->bi_buffer, bi->bi_used, (size_t)1, bi->bi_fp) != 1)

src/version.c

@@ -769,6 +769,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    988,
 /**/
     987,
 /**/