fix #15698 (#15699)

* fix in the net.`$` to print zeros that are not in the compressed group

* Update lib/pure/net.nim

Co-authored-by: Andreas Rumpf <rumpf_a@web.de>

* Update net.nim

Co-authored-by: Andreas Rumpf <rumpf_a@web.de>

lib/pure/net.nim

@@ -1827,6 +1827,10 @@ proc `$`*(address: IpAddress): string =
                 result.add(chr(uint16(ord('a'))+val-0xA))
               afterLeadingZeros = true
             mask = mask shr 4
+
+          if not afterLeadingZeros:
+            result.add '0'
+
           printedLastGroup = true
 
 proc dial*(address: string, port: Port,