exmdb_provider: emit log message when an OP_MOVE/OP_COPY rule cannot proceed

Author: jengelh

exch/exmdb_provider/message.cpp

@@ -3204,6 +3204,10 @@ static bool op_move_same(BOOL b_oof, const char *from_address,
 	if (!common_util_check_folder_id(psqlite, dst_fid, &b_exist))
 		return FALSE;
 	if (!b_exist) {
+		fprintf(stderr, "W-1978: inbox \"%s\": while processing msgid %llxh (folder %llxh), "
+		        "an OP_MOVE/OP_COPY rule was disabled "
+		        "because target folder %llxh does not exist\n",
+		        znul(account), LLU(message_id), LLU(folder_id), LLU(dst_fid));
 		message_make_deferred_error_message(account,
 			psqlite, folder_id, message_id, prnode->id,
 			RULE_ERROR_MOVECOPY, block.type,