Rectangle of text drawn on strip could be inverted, which triggered
assert in `UI_view2d_view_to_region_rcti_clip()`.
This was because scrollbar width was added to left side of rectangle.
Since now scrollers are drawn on right side, this offset is replaced
with same offset as is used for strip handles. Both sides of rectangle
are clamped to same range, so it will not get inverted.
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