pybootchart: Avoid divide by zero
Avoid a rare divide by zero error if there isn't data point spread.
[YOCTO #14547]
Signed-off-by: 
Richard Purdie <richard.purdie@linuxfoundation.org>
Loading
Avoid a rare divide by zero error if there isn't data point spread.
[YOCTO #14547]
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>