When the QoS stats are reset (e.g. changing the source) the counters for
dropped + rendered frames are reset to zero which result in negative values
for their difference. This results in max-fps getting pegged at an extremely
high value.
```
fpsdisplaysink.c:373:display_current_fps:<fpsdisplaysink0> Updated max-fps to 36840705952231460864.000000
```
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/3989>
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