Fix compilation problems in 'amp' plugin.

Four instances where 'default:' is at the end of a block replaced with
'default: break;' (reported by mscherer).

One typo where [j] should have been [1] (array out of bounds error).

Missing <unistd.h> includes for _exit(), and <string.h> for memcpy().

dll/amp/util.c

@@ -10,6 +10,7 @@
 #include <stdio.h>
 #include <stdarg.h>
 #include <string.h>
+#include <unistd.h>
 
 #include "audio.h"