Bug#21042 mysql client segfaults on importing a mysqldump export

 - Use strmake, that will both protect the buffer and make sure it's terminated by a zero
 - Add test case

client/mysql.cc

@@ -2858,7 +2858,7 @@ com_connect(String *buffer, char *line)
   bzero(buff, sizeof(buff));
   if (buffer)
   {
-    strxnmov(buff, sizeof(buff), line, NullS);
+    strmake(buff, line, sizeof(buff));
     tmp= get_arg(buff, 0);
     if (tmp && *tmp)
     {

mysql-test/r/mysql.result

@@ -114,4 +114,5 @@ a	int(11)	YES		NULL
 b	varchar(255)	YES		NULL	
 c	int(11)	YES		NULL	
 drop table t1;
+ERROR 1049 (42000) at line 1: Unknown database 'verylongdatabasenamethatshouldblowthe256byteslongbufferincom_con'
 End of 5.0 tests

mysql-test/t/mysql.test

@@ -86,6 +86,12 @@ create table t1(a int, b varchar(255), c int);
 --exec $MYSQL test -e "desc t1\g"
 drop table t1;
 
+#
+# Bug#21042  	mysql client segfaults on importing a mysqldump export
+#
+--error 1
+--exec $MYSQL test -e "connect verylongdatabasenamethatshouldblowthe256byteslongbufferincom_connectfunctionxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxkxendcccccccdxxxxxxxxxxxxxxxxxkskskskskkskskskskskskskskskskkskskskskkskskskskskskskskskend" 2>&1
+
 --echo End of 5.0 tests