patch 8.0.0365: might free a dict item that wasn't allocated

Problem:    Might free a dict item that wasn't allocated.
Solution:   Call dictitem_free(). (Nikolai Pavlov)  Use this for
            b:changedtick.
diff --git a/src/edit.c b/src/edit.c
index c4e7ddd..9a82432 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 != CHANGEDTICK(curbuf)
 # 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 = CHANGEDTICK(curbuf);
     }
 #endif