fcl-base: Fix mistake in TStringWriter constructor
Summary
TStringWriter.Create(aBuilder: TStringBuilder) overloaded constructor accepts a TStringBuilder instance but it's unused.
What is the current bug behavior?
The passed in aBuilder is ignored and a new TStringBuilder instance is created instead.
What is the behavior after applying this patch?
aBuilder is correctly assigned to FBuilder class field, no instance is created.
Relevant logs and/or screenshots
N/A