patch 8.0.0334: can't access b:changedtick from a dict reference

Problem:    Can't access b:changedtick from a dict reference.
Solution:   Make changedtick a member of the b: dict. (inspired by neovim
            #6112)
diff --git a/src/edit.c b/src/edit.c
index bc8652b..a37261f 100644
--- a/src/edit.c
+++ b/src/edit.c
@@ -1668,7 +1668,7 @@
 #ifdef FEAT_AUTOCMD
     /* Trigger TextChangedI if b_changedtick differs. */
     if (ready && has_textchangedI()
-	    && last_changedtick != curbuf->b_changedtick
+	    && last_changedtick != *curbuf->b_changedtick
 # ifdef FEAT_INS_EXPAND
 	    && !pum_visible()
 # endif
@@ -1677,7 +1677,7 @@
 	if (last_changedtick_buf == curbuf)
 	    apply_autocmds(EVENT_TEXTCHANGEDI, NULL, NULL, FALSE, curbuf);
 	last_changedtick_buf = curbuf;
-	last_changedtick = curbuf->b_changedtick;
+	last_changedtick = *curbuf->b_changedtick;
     }
 #endif