Checkmk Werk 15849: Filesystem checks: Avoid crash if device reports negative free space

ID: 15849 Title: Filesystem checks: Avoid crash if device reports negative free space Component: Checks & agents Level: 1 Class: Bug fix Version: 2.3.0b1 A negative value for the free space is of course nonsense. However, if a device reported this, Checkmk might have crashed with C+: ValueError("Cannot render negative timespan") C-: when attempting to compute the time left until the filesystem is full. Now, we instead report a value of 0 seconds in this case, st. users receive informative notifications about the problem.