patch 8.2.4235: invalid check for NULL pointer

Problem:    Invalid check for NULL pointer.
Solution:   Remove the check.
diff --git a/src/getchar.c b/src/getchar.c
index 49eb3d7..6602eea 100644
--- a/src/getchar.c
+++ b/src/getchar.c
@@ -254,7 +254,7 @@
 {
     int len;
 
-    if (buf->bh_curr == NULL || buf->bh_curr->b_str == NULL)
+    if (buf->bh_curr == NULL)
 	return;  // nothing to delete
     len = (int)STRLEN(buf->bh_curr->b_str);
     if (len >= slen)