N°3717 Improve iTop object history API (#192)

This fixes a major flaw in the history API that was causing "phantom" CMDBChange records (without any CMDBChangeOp attached). That was happening especially in iProcess impl.
For example this lead to the creation of the combodo-cmdbchange-cleaner module in the Mail To Ticket extension.

The modifications in detail : 
- We can now pass a non persisted CMDBChange instance to \CMDBObject::SetCurrentChange
- No persistence done in \CMDBObject::CreateChange anymore
- Persistence of the attached CMDChange will be done if necessary in CMDBChangeOp::OnInsert
- New CMDBObject::SetCurrentChangeFromParams helper method to ease resetting the current change

core/cmdbchangeop.class.inc.php

@@ -63,22 +63,30 @@ class CMDBChangeOp extends DBObject
 
 	/**
 	 * Describe (as a text string) the modifications corresponding to this change
-	 */	 
+	 */
 	public function GetDescription()
 	{
 		return '';
 	}
 
 	/**
-	 * Safety net: in case the change is not given, let's guarantee that it will
-	 * be set to the current ongoing change (or create a new one)	
-	 */	
+	 * Safety net:
+	 * * if change isn't persisted yet, use the current change and persist it if needed
+	 * * in case the change is not given, let's guarantee that it will be set to the current ongoing change (or create a new one)
+	 *
+	 * @since 2.7.7 3.0.2 3.1.0 N°3717 do persist the current change if needed
+	 */
 	protected function OnInsert()
 	{
-		if ($this->Get('change') <= 0)
-		{
-			$this->Set('change', CMDBObject::GetCurrentChange());
+		$iChange = $this->Get('change');
+		if (($iChange <= 0) || (is_null($iChange))) {
+			$oChange = CMDBObject::GetCurrentChange();
+			if ($oChange->IsNew()) {
+				$oChange->DBWrite();
+			}
+			$this->Set('change', $oChange);
 		}
+
 		parent::OnInsert();
 	}
 }