strformat produces wrong output for negative zero if sign is requested

[skilchen]

import strformat
echo fmt"{-0.0:+f}"
echo fmt"{-0.0:+e}"
echo fmt"{-0.0:+g}"

produces:

+-0n.000000
+-0.000000e+00
+-0

strformat shouldn't add the '+' in this case.

And btw. if you try to run this on the js backend, you get something like:

res_121201 = f_121023.toFixed(precision_121030);
			                      ^

RangeError: toFixed() digits argument must be between 0 and 100

this is due to strutils.parseBiggestFloat which in the defined(js) branch doesn't handle the case precision < 0.

[skilchen]

has been fixed in #7954. thanks @Varriount for the support!