patch 8.0.0607: after :bwipe + :new bufref might still be valid

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.

src/version.c

@@ -764,6 +764,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    607,
 /**/
     606,
 /**/