command/all: don't create new Response instance in exception handler

The new Response instance in the `catch` block didn't have the
`command` attribute set, so the error response didn't indicate which
command had failed, which however is required in the MPD protocol.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/628

NEWS

@@ -6,6 +6,8 @@ ver 0.21.14 (not yet released)
 * player
   - fix crash after song change
   - fix seek position after restarting the decoder
+* protocol
+  - include command name in error responses
 
 ver 0.21.13 (2019/08/06)
 * input

src/command/AllCommands.cxx

@@ -363,7 +363,7 @@ command_checked_lookup(Response &r, unsigned permission,
 
 CommandResult
 command_process(Client &client, unsigned num, char *line) noexcept
-try {
+{
 	Response r(client, num);
 
 	/* get the command name (first word on the line) */
@@ -391,6 +391,7 @@ try {
 	char *argv[COMMAND_ARGV_MAX];
 	Request args(argv, 0);
 
+	try {
 		/* now parse the arguments (quoted or unquoted) */
 
 		while (true) {
@@ -415,8 +416,8 @@ try {
 			return CommandResult::ERROR;
 
 		return cmd->handler(client, args, r);
-} catch (...) {
-	Response r(client, num);
+	} catch (...) {
 		PrintError(r, std::current_exception());
 		return CommandResult::ERROR;
+	}
 }