Raise ValueError when WMF inch is zero

[radarhere]

Resolves #8597

The issue is concerned that a ZeroDivisionError may be raised if self._inch is zero.

Pillow/src/PIL/WmfImagePlugin.py

Lines 104 to 107 in a7338f8

	size = (
	(x1 - x0) * self.info["dpi"] // self._inch,
	(y1 - y0) * self.info["dpi"] // self._inch,
	)

This raises a ValueError of "Invalid inch" first.