[processing] made xgrids parameter in raster calculator optional

Author: volaya

python/plugins/processing/algs/saga/RasterCalculator.py

@@ -61,7 +61,7 @@ def defineCharacteristics(self):
         self.group = SagaGroupNameDecorator.getDecoratedName(self.undecoratedGroup)
         self.addParameter(ParameterRaster(self.GRIDS, 'Main input layers'))
         self.addParameter(ParameterMultipleInput(self.XGRIDS, 'Additional layers',
-                          ParameterMultipleInput.TYPE_RASTER, False))
+                          ParameterMultipleInput.TYPE_RASTER, True))
         self.addParameter(ParameterString(self.FORMULA, "Formula"))
         self.addOutput(OutputRaster(self.RESULT, "Result"))