patch 8.2.3407: using uninitialized memory with "let g:['bar'] = 2"

Problem:    Using uninitialized memory with "let g:['bar'] = 2".
Solution:   Initialize v_type of a new dict item.

src/dict.c

@@ -229,6 +229,7 @@ dictitem_alloc(char_u *key)
 	STRCPY(di->di_key, key);
 	di->di_flags = DI_FLAGS_ALLOC;
 	di->di_tv.v_lock = 0;
+	di->di_tv.v_type = VAR_UNKNOWN;
     }
     return di;
 }

src/version.c

@@ -755,6 +755,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    3407,
 /**/
     3406,
 /**/