Remove the underscore from printer name if it is the last and not the only character

[darkvision77]

If the backend reports the device name “Canon LBP3200 (captusb)”, the parentheses and their contents are removed, leaving a space at the end, which is replaced with an underscore, resulting in “Canon_LBP3200_”.
This underscore at the end is extremely annoying.

Similar code in cups/dest.c:

cups/cups/dest.c

Lines 3971 to 3977 in 2f6411e

	//
	// Remove an underscore if it is the last character and isn't the only
	// character in the name...
	//
	if (nameptr > (name + 1) && nameptr[-1] == '_')
	nameptr --;

You can test this patch using a dummy backend:

#!/bin/sh
echo 'direct test://test1 "Canon LBP3200" "Canon LBP3200 (captusb)" "MFG:Canon;MDL:LBP3200;CMD:CAPT;VER:1.0;CLS:PRINTER;DES:Canon LBP3200" ""'
echo 'direct test://test2 "Canon LBP3200" "_" "MFG:Canon;MDL:LBP3200;CMD:CAPT;VER:1.0;CLS:PRINTER;DES:Canon LBP3200" ""'

Ref darkvision77/captppd#4 (comment)