vim-patch:8.0.0607 (#6879)

Problem:    When creating a bufref, then using :bwipe and :new it might get
            the same memory and bufref_valid() returns true.
Solution:   Add br_fnum to check the buffer number didn't change.

45e5fd135d

src/nvim/buffer_defs.h

@@ -12,6 +12,7 @@ typedef struct file_buffer buf_T; // Forward declaration
 // bufref_valid() only needs to check "buf" when the count differs.
 typedef struct {
   buf_T *br_buf;
+  int    br_fnum;
   int    br_buf_free_count;
 } bufref_T;