[Processing] Manage default value for parameter

To finalize commit 3472ac8 update processing to well manage default value

Author: rldhont

python/plugins/processing/core/Processing.py

@@ -299,7 +299,7 @@ def runAlgorithm(algOrName, onFinish, *args, **kwargs):
             # fill any missing parameters with default values if allowed
             for param in alg.parameters:
                 if param.name not in setParams:
-                    if not param.setValue(None):
+                    if not param.setDefaultValue():
                         print ('Error: Missing parameter value for parameter %s.' % (param.name))
                         QgsMessageLog.logMessage(Processing.tr('Error: Missing parameter value for parameter {0}.').format(param.name), Processing.tr("Processing"))
                         ProcessingLog.addToLog(