On german/french/spanish keyboards, typing [ requires modifier
keys like AltGr, so the `mod==0` condition is wrong.
Fixes#2573
ch != 0 is useless because IsPrint is implemented this way:
if uint32(r) <= MaxLatin1 {
return properties[uint8(r)]&128 != 0
}
with properties[0] set to 1 (so, bit 7 not set)
-> 0 is not printable.