Clamp ProgressBar completion to the drawable range - #1388

ProgressBar raised or drew the wrong bar when current or done was out of range or not finite:

• done <= 0 or NaN, and a NaN ratio, now render an empty bar.
• current is clamped to [0, done], including infinite values, so a negative current no longer draws a part-filled bar or raises IndexError when satt is set.
• An operand too large for a float draws a full bar when current exceeds done, and an empty one otherwise.
• get_text() and render() share the clamped computation.

Checklist

• I've ensured that similar functionality has not already been implemented
• I've ensured that similar functionality has not earlier been proposed and declined
• I've branched off the master branch
• I've merged fresh upstream into my branch recently
• I've ran tox successfully in local environment
• I've included docstrings and/or documentation and/or examples for my code (if this is a new feature)