hashmap: rework hashmap_clear() to be more defensive

Let's first remove an item from the hashmap and only then destroy it.
This makes sure that destructor functions can mdoify the hashtables in
their own codee and we won't be confused by that.

src/basic/hashmap.h

@@ -191,7 +191,11 @@ static inline void *ordered_hashmap_remove2(OrderedHashmap *h, const void *key,
         return hashmap_remove2(PLAIN_HASHMAP(h), key, rkey);
 }
 
-void *hashmap_remove_value(Hashmap *h, const void *key, void *value);
+void *internal_hashmap_remove_value(HashmapBase *h, const void *key, void *value);
+static inline void *hashmap_remove_value(Hashmap *h, const void *key, void *value) {
+        return internal_hashmap_remove_value(HASHMAP_BASE(h), key, value);
+}
+
 static inline void *ordered_hashmap_remove_value(OrderedHashmap *h, const void *key, void *value) {
         return hashmap_remove_value(PLAIN_HASHMAP(h), key, value);
 }