Bug #41943: mysqlbinlog.exe crashes if --hexdump option is used

The --hexdump option crashed mysqlbinlog when used together  
with the --read-from-remote-server option due to use of  
uninitialized memory.  
  
Since Log_event::print_header() relies on temp_buf to be  
initialized when the --hexdump option is present,  
dump_remote_log_entries() was fixed to setup temp_buf to point  
to the start of a binlog event as done in  
dump_local_log_entries().  
 
The root cause of this bug is identical to the one for 
bug #17654. The latter was fixed in 5.1 and up, so this 
patch is backport of the patches for bug #17654 to 5.0. 
 
Only 5.0 needs a changelog entry. 

client/mysqlbinlog.cc:
  Fixed dump_remote_log_entries() so that temp_buf is initialized 
  as it may be used later by Log_event::print_header() if the 
  --hexdump option is present.
mysql-test/r/mysqlbinlog.result:
  Added a test case for bug #41943.
mysql-test/t/mysqlbinlog.test:
  Added a test case for bug #41943.

mysql-test/r/mysqlbinlog.result

@@ -380,4 +380,6 @@ IS NOT NULL
 1
 *** Unsigned server_id 4294967295 is found: 1 ***
 SET @@global.server_id= 1;
+RESET MASTER;
+FLUSH LOGS;
 End of 5.0 tests