fix(PISerial): break infinite loop when readDevice returns <= 0

In the blocking read path (timeout_ms <= 0), the while loop had no
exit condition for readDevice() returning 0 (EOF) or -1 (error).
This caused an infinite busy-loop at 100% CPU. Added 'else break'
to exit the loop on read failure, matching the timeout branch
which already handles this case.

libs/main/io_devices/piserial.cpp

@@ -513,7 +513,10 @@ bool PISerial::read(void * data, int size, double timeout_ms) {
 		all     = readDevice(data, 1);
 		while (all < size) {
 			ret = readDevice(&((uchar *)data)[all], size - all);
-			if (ret > 0) all += ret;
+			if (ret > 0)
+				all += ret;
+			else
+				break;
 		}
 		setOption(BlockingRead, br);
 		received(data, all);