Timeline: Fix segfault in control sequence playback

Closes #173

timeline/src/Engine/Control_Sequence.C

@@ -85,8 +85,12 @@ Control_Sequence::play ( sample_t *buf, nframes_t frame, nframes_t nframes )
             incr = 0.0f;
         
         float v = y1 + start * incr;
+
+        if ( ! n )
+            /* buffer's full, no point in continuing */
+            break;
         
-        for ( nframes_t i = start; i < len && n--; ++i, v += incr )
+        for ( nframes_t i = start; i < len && n && n--; ++i, v += incr )
             *(buf++) = v;
     }
 

timeline/src/Timeline.C

@@ -2208,16 +2208,15 @@ 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 );
         
         t->process_osc();
     }
-
-    /* unlock(); */
+    
+    sequence_lock.unlock();
 }