vmui: incorrectly displayed graph in certain cases

[valyala]

Describe the bug
vmui incorrectly displays graphs in certain cases.

To Reproduce

1. Run a query q - https://play.victoriametrics.com/select/accounting/1/6a716b0f-38bc-4856-90ce-448fd713e3fe/prometheus/graph/?g0.range_input=1d&g0.end_input=2022-01-05T20%3A06%3A35&g0.step_input=93.254&g0.tab=chart&g0.expr=sum(100*rate(process_cpu_seconds_total))%3E5.4 . All the gaps on the graph are displayed correctly when comparing to https://play.victoriametrics.com/select/accounting/1/6a716b0f-38bc-4856-90ce-448fd713e3fe/prometheus/graph/?g0.range_input=1d&g0.end_input=2022-01-05T20%3A06%3A35&g0.step_input=93.254&g0.tab=chart&g0.expr=sum(100*rate(process_cpu_seconds_total))

2. Add default 0 to the end of the query - https://play.victoriametrics.com/select/accounting/1/6a716b0f-38bc-4856-90ce-448fd713e3fe/prometheus/graph/?g0.range_input=1d&g0.end_input=2022-01-05T20%3A06%3A35&g0.step_input=93.254&g0.tab=chart&g0.expr=sum(100*rate(process_cpu_seconds_total))%3E5.4%20default%200 . The graph is displayed incorrectly - the graph values are limited in the range 0...1. This is the bug in vmui, since VictoriaMetrics returns the correct data points for this query.

Expected behavior
The default 0 must fill gaps from the graph at step 1 with zeroes, while leaving the rest of the graph the same as at the step 1

Version
Commit c70c064 (the latest one now).

[valyala]

Additional bug - when adding default -1 to the query, then points with -1 value aren't visible on the graph - https://play.victoriametrics.com/select/accounting/1/6a716b0f-38bc-4856-90ce-448fd713e3fe/prometheus/graph/?g0.range_input=1d&g0.end_input=2022-01-05T20%3A06%3A35&g0.step_input=93.254&g0.tab=chart&g0.expr=sum(100*rate(process_cpu_seconds_total))%3E5.4%20default%20-1

[valyala]

This issue has been fixed in v1.72.0. Closing it.