core: fix zero-length malloc of an hashtable item with type "buffer"

ChangeLog.asciidoc

@@ -15,6 +15,7 @@ http://weechat.org/files/releasenotes/ReleaseNotes-devel.html[release notes]
 
 == Version 1.0 (under dev)
 
+* core: fix zero-length malloc of an hashtable item with type "buffer"
 * core: fix memory leak on /upgrade when file signature in upgrade file is
   invalid
 * core: fix memory leak in completion of config options values

src/core/wee-hashtable.c

@@ -270,7 +270,7 @@ hashtable_alloc_type (enum t_hashtable_type type,
             *size = sizeof (void *);
             break;
         case HASHTABLE_BUFFER:
-            if (value)
+            if (value && (size_value > 0))
             {
                 *pointer = malloc (size_value);
                 if (*pointer)