patch 8.2.4236: accessing freed memory

Problem:    Accessing freed memory.
Solution:   Set the bh_curr pointer to NULL.

src/getchar.c

@@ -110,6 +110,7 @@ free_buff(buffheader_T *buf)
 	vim_free(p);
     }
     buf->bh_first.b_next = NULL;
+    buf->bh_curr = NULL;
 }
 
 /*

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    4236,
 /**/
     4235,
 /**/