Merge pull request #18 from jerryneedell/jerryn_fix_byte

 fix potential byte overflow exceptions

Author: dhalbert

adafruit_sdcard.py

@@ -230,10 +230,10 @@ def _cmd(self, cmd, arg=0, crc=0, response_buf=None, data_block=True, wait=True)
         # create and send the command
         buf = self._cmdbuf
         buf[0] = 0x40 | cmd
-        buf[1] = arg >> 24
-        buf[2] = arg >> 16
-        buf[3] = arg >> 8
-        buf[4] = arg
+        buf[1] = (arg >> 24) & 0xff
+        buf[2] = (arg >> 16) & 0xff
+        buf[3] = (arg >> 8) & 0xff
+        buf[4] = arg & 0xff
         buf[5] = crc
 
         with self._spi as spi: