Problem: Clamp for height in floating windows enforced no more than
editor height - 1, disallowing full editor height floating windows when
using cmdheight=0
Solution: Clamp to full height, removing the -1. Tested to give the
intended results with cmdheight=0, 1, or more than 1. This also
inadvertently fixes a rendering error with cmdheight >1 where the
bottom border would be overlapped by the cmdline.
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