uru4000: Fix integer overflow in imaging_run_state()

‘img->key_number’ variable is originally from the device through bulk
endpoint of USB. The variable is immediately assigned to ‘buf[0]’ for
sending to control endpoint of the device. Here, integer overflow may
occur when the ‘img->key_number’ attempts to assign a value that is
outside of type range of ‘char’ to the ‘buf[0]’
2 jobs for fix-int-overflow in 8 minutes and 5 seconds (queued for 3 seconds)
latest
Status Job ID Name Coverage
  Build
passed #131452
build

00:02:13

 
  Test
passed #131453
flatpak master

00:05:52