Fix double-free / heap corruption during SQLDisconnect cleanup (#189)#190
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…resql-interfaces#189) CC_cleanup() was freeing statement and descriptor objects via SC_Destructor(), but the ODBC Driver Manager still held handles to them. When the DM later called SQLFreeStmt(SQL_DROP) via SQLFreeHandle(), the driver dereferenced freed memory, causing the double-free detected by Application Verifier with Page Heap enabled. Fix by detaching statements/descriptors in CC_cleanup() without freeing them. The DM will free them later through the normal SQLFreeHandle path. Also allow SQLFreeStmt(SQL_DROP) to proceed when hdbc is NULL (the expected state after disconnect), and remove misleading error-return logic in SC_Destructor that reported failure after already freeing.
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CC_cleanup() was freeing statement and descriptor objects via SC_Destructor(), but the ODBC Driver Manager still held handles to them. When the DM later called SQLFreeStmt(SQL_DROP) via SQLFreeHandle(), the driver dereferenced freed memory, causing the double-free detected by Application Verifier with Page Heap enabled.
Fix by detaching statements/descriptors in CC_cleanup() without freeing them. The DM will free them later through the normal SQLFreeHandle path. Also allow SQLFreeStmt(SQL_DROP) to proceed when hdbc is NULL (the expected state after disconnect), and remove misleading error-return logic in SC_Destructor that reported failure after already freeing.