[time.hms.nonmembers] Fix editorial error in hh_mm_ss operator<< (only

stream to 'os' once). This formulation was proposed by Howard Hinnant
on the lib reflector.

Author: zygoloid

source/time.tex

@@ -8039,9 +8039,10 @@
 \effects
 Equivalent to:
 \begin{codeblock}
-if (hms.is_negative())
-  os << @\placeholder{STATICALLY-WIDEN}@<charT>("-");
-return os << format(os.getloc(), @\placeholder{STATICALLY-WIDEN}@<charT>("{:%T}"), hms);
+return os << format(os.getloc(),
+                    hms.is_negative() ? @\placeholder{STATICALLY-WIDEN}@<charT>("-{:%T}")
+                                      : @\placeholder{STATICALLY-WIDEN}@<charT>("{:%T}"),
+                    abs(hms.to_duration()));
 \end{codeblock}
 
 \pnum