patch 7.4.870

Problem:    May get into an invalid state when using getchar() in an
            expression mapping.
Solution:   Anticipate mod_mask to change. (idea by Yukihiro Nakadaira)

src/getchar.c

@@ -1630,13 +1630,16 @@ vgetc()
       last_recorded_len = 0;
       for (;;)			/* this is done twice if there are modifiers */
       {
+	int did_inc = FALSE;
+
 	if (mod_mask)		/* no mapping after modifier has been read */
 	{
 	    ++no_mapping;
 	    ++allow_keys;
+	    did_inc = TRUE;	/* mod_mask may change value */
 	}
 	c = vgetorpeek(TRUE);
-	if (mod_mask)
+	if (did_inc)
 	{
 	    --no_mapping;
 	    --allow_keys;

src/version.c

@@ -741,6 +741,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    870,
 /**/
     869,
 /**/