Timeline: Fix segfault in control sequence playback

Closes #173

timeline/src/Engine/Control_Sequence.C

@@ -86,7 +86,11 @@ Control_Sequence::play ( sample_t *buf, nframes_t frame, nframes_t nframes )
         
         float v = y1 + start * incr;
 
-        for ( nframes_t i = start; i < len && n--; ++i, v += incr )
+        if ( ! n )
+            /* buffer's full, no point in continuing */
+            break;
+        
+        for ( nframes_t i = start; i < len && n && n--; ++i, v += incr )
             *(buf++) = v;
     }
 

timeline/src/Timeline.C

@@ -2208,9 +2208,8 @@ Timeline::process_osc ( void )
 {
     THREAD_ASSERT( OSC );
 
-    /* rdlock(); */
+    sequence_lock.rdlock();
 
-    /* reconnect OSC signals */
     for ( int i = tracks->children(); i-- ; )
     {
         Track *t = (Track*)tracks->child( i );
@@ -2218,6 +2217,6 @@ Timeline::process_osc ( void )
         t->process_osc();
     }
     
-    /* unlock(); */
+    sequence_lock.unlock();
 }