DAP: Change comment getter for user comment to retrieve string directly from control

The comment getter is called from the NWB Export that is also used for old experiments.
The previous DAG_GetTextualValue tries to use the GUIState wave that does not know the
possibly old control and fails for that case.

This workaround (to retrieve the value directly) is a not suited for generic use.

Author: MichaelHuth

Packages/MIES/MIES_DAEphys.ipf

@@ -4023,7 +4023,7 @@ static Function DAP_AddUserComment(string device)
 		return NaN
 	endif
 
-	comment = DAG_GetTextualValue(device, "SetVar_DataAcq_Comment")
+	comment = GetSetVariableString(device, "SetVar_DataAcq_Comment")
 
 	if(isEmpty(comment))
 		return NaN