MDEV-35224 ASAN error in mariadb client with \c

Mariadb monitor when a line is cancelled, provided
its more than one line, passes that text to the
add_history of libedit. This string that has been
passed however isn't null terminated resulting
in an ASAN error within the libedit code.

fix_history where the add_history is called
is called by the com_clear, associated with
the \c command, and com_go. An using the c_ptr
adds a null character onto the end of the string.

Author: grooverdan

client/mysql.cc

@@ -2876,7 +2876,9 @@ static void fix_history(String *final_command)
     ptr++;
   }
   if (total_lines > 1)			
-    add_history(fixed_buffer.ptr());
+  {
+    add_history(fixed_buffer.c_ptr());
+  }
 }
 
 /*