Fix placeholder for 0 width textinputs

[ShadiestGoat]

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Fixes #950

The issue is that the placeholder arr (p) was made using width + 1. Width = 0 (and, technically, width < 0) are valid widths indicating unlimited width. There is even a comment later in the view that makes it sound like this is the intentional behaviour:

if there is no width, the placeholder can be any length

However, if w = 0, then the p will be 1 rune in length rather than unlimited