[processing] Add some missing sources to expression contexts

Author: nyalldawson

python/plugins/processing/algs/qgis/Aggregate.py

@@ -170,7 +170,7 @@ def prepareAlgorithm(self, parameters, context, feedback):
         return True
 
     def processAlgorithm(self, parameters, context, feedback):
-        expr_context = self.createExpressionContext(parameters, context)
+        expr_context = self.createExpressionContext(parameters, context, self.source)
         self.group_by_expr.prepare(expr_context)
 
         # Group features in memory layers

python/plugins/processing/algs/qgis/RandomPointsPolygons.py

@@ -115,7 +115,7 @@ def processAlgorithm(self, parameters, context, feedback):
         if expression.hasParserError():
             raise QgsProcessingException(expression.parserErrorString())
 
-        expressionContext = self.createExpressionContext(parameters, context)
+        expressionContext = self.createExpressionContext(parameters, context, source)
         if not expression.prepare(expressionContext):
             raise QgsProcessingException(
                 self.tr('Evaluation error: {0}').format(expression.evalErrorString()))