functionObjects::writeObjects: Changed the default executeAtStart to 'no'

This avoids attempting to write temporary fields before they have been created.
The executeAtStart can be set to 'yes' in the writeObjects dictionary or the

functions
{
    #includeFunc writeObjects(executeAtStart = yes, <field1>, <field2>...)
}

src/OpenFOAM/db/functionObjects/functionObject/functionObject.C

@@ -130,7 +130,8 @@ bool Foam::functionObject::read(const dictionary& dict)
 
     if (!postProcess)
     {
-        executeAtStart_ = dict.lookupOrDefault<Switch>("executeAtStart", true);
+        executeAtStart_ =
+            dict.lookupOrDefault<Switch>("executeAtStart", executeAtStart_);
     }
 
     return true;