ngircd.c, main(): use strlcat() instead of strcat()

This fixes the following warning on OpenBSD 5.3:

 ngircd.o(.text+0xeb4): In function `main':
  src/ngircd/ngircd.c:300: warning: strcat() is almost always misused,
                                    please use strlcat()

Thanks to Götz Hoffart for reporting this!

src/ngircd/ngircd.c

@@ -297,7 +297,7 @@ main(int argc, const char *argv[])
 			 PROTOVER, PROTOIRCPLUS, PACKAGE_NAME, PACKAGE_VERSION,
 			 IRCPLUSFLAGS);
 #ifdef ZLIB
-		strcat(NGIRCd_ProtoID, "Z");
+		strlcat(NGIRCd_ProtoID, "Z", sizeof NGIRCd_ProtoID);
 #endif
 		if (Conf_OperCanMode)
 			strcat(NGIRCd_ProtoID, "o");