Update safety histogram x domain settings that control the width of the bar

[nandriychuk]

Fix the custom mark for x domain when drawing the bars with the range of 0.

Test notes

• Use the x-axis-tick-labels branch to test this issue.
• Add a USUBJID filter.
• Select 01-021 in the filter dropdown.
• Hit the zoom button.
• The bar should be centered on the underlying value (~47) and have a "normal" width, e.g. not too thin, not too thick, but just right.

[dschwentker]

Tested and passed