Minor allocation hook corrections.

archivers/zip.c

@@ -192,8 +192,13 @@ static voidpf zlibPhysfsAlloc(voidpf opaque, uInt items, uInt size)
     PHYSFS_allocator *allocator = __PHYSFS_getAllocator();
     size_t total = (items * size) + sizeof (PHYSFS_memhandle);
     PHYSFS_memhandle h = allocator->malloc(total);
-    char *ptr = (char *) allocator->lock(h);
-    PHYSFS_memhandle *ph = (PHYSFS_memhandle *) ptr;
+    char *ptr;
+    PHYSFS_memhandle *ph;
+    if (h == NULL)
+        return(NULL);
+
+    ptr = (char *) allocator->lock(h);
+    ph = (PHYSFS_memhandle *) ptr;
     *ph = h; /* tuck the memhandle in front of the memory block... */
     return(ptr + sizeof (PHYSFS_memhandle));
 } /* zlibPhysfsAlloc */

physfs.h

@@ -1834,7 +1834,9 @@ __EXPORT__ int PHYSFS_writeUBE64(PHYSFS_file *file, PHYSFS_uint64 val);
  *  because it's convenient for systems to have handles be the same size
  *  as a pointer, but they shouldn't be assumed to point to valid memory
  *  (or to memory at all). The allocator in use will convert from memhandles
- *  to valid pointers to allocated memory.
+ *  to valid pointers to allocated memory. A memhandle of NULL is considered
+ *  to be bogus (so malloc can return a NULL handle), even though it's not
+ *  technically a NULL pointer in itself.
  *
  * \sa PHYSFS_allocator
  * \sa PHYSFS_setAllocator