legacy stash: fix "rudimentary backport of -q"

When this developer backported support for `--quiet` to the scripted
version of `git stash` in 8059005 (stash: optionally use the scripted
version again, 2018-12-20), it looked like a sane choice to use `eval`
to execute the command line passed in via the parameter list of
`maybe_quiet`.

However, that is not what we should have done, as that command-line was
already in the correct shape.

This can be seen very clearly when passing arguments with special
characters, like

	git stash -- ':(glob)**/*.txt'

Since this is exactly what we want to test in the next commit (where we
fix this very incantation with the built-in stash), let's fix the legacy
scripted version of `git stash` first.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: dscho

git-legacy-stash.sh

@@ -86,17 +86,17 @@ maybe_quiet () {
 		shift
 		if test -n "$GIT_QUIET"
 		then
-			eval "$@" 2>/dev/null
+			"$@" 2>/dev/null
 		else
-			eval "$@"
+			"$@"
 		fi
 		;;
 	*)
 		if test -n "$GIT_QUIET"
 		then
-			eval "$@" >/dev/null 2>&1
+			"$@" >/dev/null 2>&1
 		else
-			eval "$@"
+			"$@"
 		fi
 		;;
 	esac