IRC_xLINE(): output an error message for unexpected "lines"

This fixes:

 irc-oper.c: In function ‘IRC_xLINE’:
 irc-oper.c:429: warning: ‘class’ may be used uninitialized in this function
 irc-oper.c:430: warning: ‘class_c’ may be used uninitialized in this function

src/ngircd/irc-oper.c

@@ -450,6 +450,11 @@ IRC_xLINE(CLIENT *Client, REQUEST *Req)
 		case 'K':
 			class = CLASS_KLINE; class_c = 'K';
 			break;
+		default:
+			Log(LOG_CRIT,
+			    "IRC_xLINE() called for unknown line: %c!? Ignored.",
+			    Req->command[0]);
+			return CONNECTED;
 	}
 
 	if (Req->argc == 1) {