patch 8.2.4236: accessing freed memory

Problem:    Accessing freed memory.
Solution:   Set the bh_curr pointer to NULL.
diff --git a/src/getchar.c b/src/getchar.c
index 6602eea..cb8a354 100644
--- a/src/getchar.c
+++ b/src/getchar.c
@@ -110,6 +110,7 @@
 	vim_free(p);
     }
     buf->bh_first.b_next = NULL;
+    buf->bh_curr = NULL;
 }
 
 /*
diff --git a/src/version.c b/src/version.c
index 49942b5..23b29da 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    4236,
+/**/
     4235,
 /**/
     4234,