Fix for Synaesthesia memory corruption

We were allocating just half the required space and consequently
writing beyond the end of the array. This consistently caused
segfaults for me when using the Synaesthesia visualiser.

This fix appears to be consistent with the code used in other projects
which were also derived from the original Synaesthia project.

e.g. GStreamer/Source/gst-plugins-ugly/gst/synaesthesia/synaescope.c

mythplugins/mythmusic/mythmusic/polygon.h

@@ -18,13 +18,13 @@ class Bitmap
         delete[] data;
         width = w;
         height = h;
-        data = new Pixel[w*h+extra];
+        data = new Pixel[2*w*h+extra];
         clear();
     }
 
     void clear()
     {
-        memset(data,0,sizeof(Pixel)*(width*height+extra));
+        memset(data,0,sizeof (Pixel)*(2*width*height+extra));
     }
 };
 #endif