Fixed bug in parsePacket where it could block indefinitely if called when no packets were available to be read.

libraries/Ethernet/Udp.cpp

@@ -120,6 +120,8 @@ void UDP::write(const uint8_t *buffer, size_t size)
 }
 
 int UDP::parsePacket()
+{
+  if (available() > 0)
   {
     //HACK - hand-parse the UDP packet using TCP recv method
     uint8_t tmpBuf[8];
@@ -136,6 +138,9 @@ int UDP::parsePacket()
     }
     return ret;
   }
+  // There aren't any packets available
+  return 0;
+}
 
 int UDP::read()
 {