Fix crash when tracing is enabled. Position after buffer was used also
direct usage of MYSQLND_STRING pointer instead of the "s" property of the
structure.
- More statistics
- Fixed endless loop - mysqlnd_stmt_next_result() returned FAIL but as it
is defined to be 1 (and PASS is 0), checking for mysqlnd_stmt_more_result()
was successful although we were expecting a FAIL.