[Chore](Job)Fix the wrong log when the export job reads fields and add more clear log information (#21490)

* [Chore](Job)Fix the wrong log when the export job reads fields and add more clear log information

* add OriginStatement .toString method

fe/fe-core/src/main/java/org/apache/doris/load/ExportJob.java

@@ -733,7 +733,7 @@ public class ExportJob implements Writable {
             stmt = (ExportStmt) SqlParserUtils.getStmt(parser, origStmt.idx);
             this.whereExpr = stmt.getWhereExpr();
         } catch (Exception e) {
-            throw new IOException("error happens when parsing create routine load stmt: " + origStmt, e);
+            throw new IOException("error happens when parsing export stmt: " + origStmt, e);
         }
     }
 

fe/fe-core/src/main/java/org/apache/doris/qe/OriginStatement.java

@@ -55,4 +55,12 @@ public class OriginStatement implements Writable {
         String json = GsonUtils.GSON.toJson(this);
         Text.writeString(out, json);
     }
+
+    @Override
+    public String toString() {
+        return "OriginStatement{"
+                + "originStmt='" + originStmt + '\''
+                + ", idx=" + idx
+                + '}';
+    }
 }