fix buffering problem in rockbox

peadar@fatlenny$ diff -Nuw apps/buffering.c.0 apps/buffering.c
--- apps/buffering.c.0  2011-01-11 00:01:50.000000000 +0000
+++ apps/buffering.c    2011-01-22 01:50:57.000000000 +0000
@@ -681,7 +681,7 @@
          * If this is true, then there's a handle even though we have still
          * data to buffer. This should NEVER EVER happen! (but it does :( ) */
         if (h->next && (overlap
-                = ringbuf_add_cross(h->widx, copy_n, next_handle)) > 0)
+                = ringbuf_add_cross(h->widx, copy_n, next_handle)) >= 0)
         {
             /* stop buffering data for now and post-pone buffering the rest */
             stop = true;
@@ -689,7 +689,11 @@
                     " copy_n:%lu overlap:%ld h1.filerem:%lu\n", __func__,
                     h->id, h->next->id, (unsigned long)copy_n, (long)overlap,
                     (unsigned long)h->filerem);
-            copy_n -= overlap;
+            if (overlap == (ssize_t)copy_n) {
+                DEBUGF("%u: buffer_handle(%d): READ NOTHING\n", thread_get_current(), handle_id);
+                return false;
+            }
+            copy_n -= overlap + 1;
         }

         /* rc is the actual amount read */