builtin-help: silently tolerate unknown keys

If for some reason the config file contains a key without a subkey like

    [man]
        foo = bar

then even a plain

    git help

produces an error message. With this patch such an entry is ignored.

Additionally, the warning about unknown sub-keys is removed. It could
become annoying if new sub-keys are introduced in the future, and then
the configuration is read by an old version of git that does not know
about it.

Signed-off-by: Johannes Sixt <j6t@kdbg.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-help.c

@@ -236,7 +236,7 @@ static int add_man_viewer_info(const char *var, const char *value)
 	const char *subkey = strrchr(name, '.');
 
 	if (!subkey)
-		return error("Config with no key for man viewer: %s", name);
+		return 0;
 
 	if (!strcmp(subkey, ".path")) {
 		if (!value)
@@ -249,7 +249,6 @@ static int add_man_viewer_info(const char *var, const char *value)
 		return add_man_viewer_cmd(name, subkey - name, value);
 	}
 
-	warning("'%s': unsupported man viewer sub key.", subkey);
 	return 0;
 }