CLEANUP: hlua: Remove obsolete branch in `hlua_alloc()`

This branch is no longer required, because the `!nsize` case is handled for any
value of `ptr` now.

see 22586524e32f14c44239063088a38ccea8abc9b7
see a5efdff93c36f75345a2a18f18bffee9b602bc7b
diff --git a/src/hlua.c b/src/hlua.c
index f433a4f..0bb9024 100644
--- a/src/hlua.c
+++ b/src/hlua.c
@@ -11529,9 +11529,6 @@
 	struct hlua_mem_allocator *zone = ud;
 	size_t limit, old, new;
 
-	if (unlikely(!ptr && !nsize))
-		return NULL;
-
 	/* a limit of ~0 means unlimited and boot complete, so there's no need
 	 * for accounting anymore.
 	 */