fix destination nodata value in gdal merge

Author: etiennesky

python/plugins/GdalTools/tools/doMerge.py

@@ -147,6 +147,8 @@ def getArguments(self):
       if self.noDataCheck.isChecked():
         arguments.append("-n")
         arguments.append(str(self.noDataSpin.value()))
+        arguments.append("-a_nodata")
+        arguments.append(str(self.noDataSpin.value()))
       if self.separateCheck.isChecked():
         arguments.append("-separate")
       if self.pctCheck.isChecked():