[PATCH 0/2] squelch some "gcc -O3 -Wmaybe-uninitialized" warnings

I happened to be compiling git with -O3 today, and noticed we generate
some warnings about uninitialized variables (I actually compile with
-Wall, but the only false positives I saw were these).

Here are patches to squelch them.

  [1/2]: error_errno: use constant return similar to error()
  [2/2]: color_parse_mem: initialize "struct color" temporary

-Peff