Description of problem:
When I start mifare-tool with no reader attached it terminates immediatly
writing that a buffer overflow was detected.


Version-Release number of selected component (if applicable):
0.1.0-2

How reproducible:
always

Steps to Reproduce:
1. $ mifare-tool
  
Actual results:
*** buffer overflow detected ***: mifare-tool terminated
======= Backtrace: =========
/lib/libc.so.6(__chk_fail+0x41)[0x477ec361]
mifare-tool[0x8048be4]
/lib/libc.so.6(__libc_start_main+0xdc)[0x47720f2c]
mifare-tool[0x80489f1]
======= Memory map: ========
00148000-0014f000 r-xp 00000000 08:06 1217378    /usr/lib/librfid.so.0.0.0
0014f000-00150000 rwxp 00007000 08:06 1217378    /usr/lib/librfid.so.0.0.0
00ae9000-00aea000 r-xp 00ae9000 00:00 0          [vdso]
08048000-0804a000 r-xp 00000000 08:06 1213443    /usr/bin/mifare-tool
0804a000-0804b000 rwxp 00002000 08:06 1213443    /usr/bin/mifare-tool
08c53000-08c74000 rwxp 08c53000 00:00 0 
476ee000-47707000 r-xp 00000000 08:06 2488382    /lib/ld-2.5.so
47707000-47708000 r-xp 00018000 08:06 2488382    /lib/ld-2.5.so
47708000-47709000 rwxp 00019000 08:06 2488382    /lib/ld-2.5.so
4770b000-47842000 r-xp 00000000 08:06 2488383    /lib/libc-2.5.so
47842000-47844000 r-xp 00137000 08:06 2488383    /lib/libc-2.5.so
47844000-47845000 rwxp 00139000 08:06 2488383    /lib/libc-2.5.so
47845000-47848000 rwxp 47845000 00:00 0 
47ac9000-47ad4000 r-xp 00000000 08:06 2293531    /lib/libgcc_s-4.1.1-20070105.so.1
47ad4000-47ad5000 rwxp 0000a000 08:06 2293531    /lib/libgcc_s-4.1.1-20070105.so.1
47d4c000-47d52000 r-xp 00000000 08:06 1225396    /usr/lib/libusb-0.1.so.4.4.4
47d52000-47d54000 rwxp 00006000 08:06 1225396    /usr/lib/libusb-0.1.so.4.4.4
b7fe0000-b7fe1000 rw-p b7fe0000 00:00 0 
b7ff8000-b7ff9000 rw-p b7ff8000 00:00 0 
bff25000-bff3b000 rw-p bff25000 00:00 0          [stack]

Expected results:
The errors above should not appear.