univalue: make spaceStr thread-safe
univalue: make spaceStr thread-safe

Simply add spaces to the existing string instead of using a
temporary.

Fixes #4756.

Infernoman/crowncoin,Crowndev/crowncoin,domob1812/crowncoin,domob1812/crowncoin,Crowndev/crowncoin,Infernoman/crowncoin,syscoin/syscoin,Infernoman/crowncoin,Crowndev/crowncoin,Crowndev/crowncoin,Infernoman/crowncoin,syscoin/syscoin,Infernoman/crowncoin,domob1812/crowncoin,syscoin/syscoin,domob1812/crowncoin,syscoin/syscoin,Infernoman/crowncoin,Crowndev/crowncoin,domob1812/crowncoin,syscoin/syscoin,domob1812/crowncoin,syscoin/syscoin,Crowndev/crowncoin,syscoin/syscoin,syscoin/syscoin