builtin-apply.c: use git_config_string() to get apply_default_whitespace

Signed-off-by: Stephan Beyer <s-beyer@gmx.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-apply.c

@@ -2981,12 +2981,8 @@ static int apply_patch(int fd, const char *filename, int inaccurate_eof)
 
 static int git_apply_config(const char *var, const char *value)
 {
-	if (!strcmp(var, "apply.whitespace")) {
-		if (!value)
-			return config_error_nonbool(var);
-		apply_default_whitespace = xstrdup(value);
-		return 0;
-	}
+	if (!strcmp(var, "apply.whitespace"))
+		return git_config_string(&apply_default_whitespace, var, value);
 	return git_default_config(var, value);
 }