It should not exit() anymore on error except on malloc failure.
Resource leaks on errors (especially I/O) are quite likely though.
Change-Id: I6fcf72fb08fc683468b390d0b8745d31ca982b48
On Windows /dev/random does not exist, so trying to open it will fail. Replace
it with rand() which is available on all supported platforms and sufficient.
Fixes mkimxboot not working, as well as Rockbox Utility "crashing" (which is in
fact its error handler calling exit(), thus terminating Rockbox Utility) on
Windows.
Change-Id: Ia164f937f329877e8f80f473f27be8c5df2a0a68
