Make swap-quote-keys better

For some reason I need two ^Qs, and it doesn't work with multi-line editing.

An alternate version like:

```
local c LBUFFER=$PREBUFFER$LBUFFER

for (( c = $#LBUFFER; c > 0; c-- )); do
if [[ $LBUFFER[c] == \' ]]; then
LBUFFER[c]=\"
break
elif [[ $LBUFFER[c] == \" ]]; then
LBUFFER[c]=\'
break
fi
done

print -rz -- $LBUFFER$RBUFFER
zle send-break
```

would, but should change that so that it only uses that way if it's multiline, otherwise with single-line input, the `send-break` causes duplicate lines.