ecpg: Refactor ecpg_log() to skip unnecessary calls to ECPGget_sqlca().

ecpg: Refactor ecpg_log() to skip unnecessary calls to ECPGget_sqlca().

Previously, ecpg_log() always called ECPGget_sqlca() to retrieve sqlca,
even though it was only needed for debug logging. This commit updates
ecpg_log() to call ECPGget_sqlca() only when debug logging is enabled.

Author: Yuto Sasaki
Reviewed-by: Alvaro Herrera, Tom Lane, Fujii Masao
Discussion: https://postgr.es/m/TY2PR01MB3628A85689649BABC9A1C6C3C1782@TY2PR01MB3628.jpnprd01.prod.outlook.com