[processing] Fix some crashes on invalid parameters

Author: nyalldawson

src/analysis/processing/qgsalgorithmextractbylocation.cpp

@@ -349,7 +349,12 @@ QgsExtractByLocationAlgorithm *QgsExtractByLocationAlgorithm::createInstance() c
 QVariantMap QgsExtractByLocationAlgorithm::processAlgorithm( const QVariantMap &parameters, QgsProcessingContext &context, QgsProcessingFeedback *feedback )
 {
   std::unique_ptr< QgsFeatureSource > input( parameterAsSource( parameters, QStringLiteral( "INPUT" ), context ) );
+  if ( !input )
+    throw QgsProcessingException( invalidSourceError( parameters, QStringLiteral( "INPUT" ) ) );
   std::unique_ptr< QgsFeatureSource > intersectSource( parameterAsSource( parameters, QStringLiteral( "INTERSECT" ), context ) );
+  if ( !intersectSource )
+    throw QgsProcessingException( invalidSourceError( parameters, QStringLiteral( "INTERSECT" ) ) );
+
   const QList< int > selectedPredicates = parameterAsEnums( parameters, QStringLiteral( "PREDICATE" ), context );
   QString dest;
   std::unique_ptr< QgsFeatureSink > sink( parameterAsSink( parameters, QStringLiteral( "OUTPUT" ), context, dest, input->fields(), input->wkbType(), input->sourceCrs() ) );

src/analysis/processing/qgsalgorithmfiledownloader.cpp

@@ -71,6 +71,8 @@ QVariantMap QgsFileDownloaderAlgorithm::processAlgorithm( const QVariantMap &par
 {
   mFeedback = feedback;
   QString url = parameterAsString( parameters, QStringLiteral( "URL" ), context );
+  if ( url.isEmpty() )
+    throw QgsProcessingException( tr( "No URL specified" ) );
   QString outputFile = parameterAsFileOutput( parameters, QStringLiteral( "OUTPUT" ), context );
 
   QEventLoop loop;

src/analysis/processing/qgsalgorithmsaveselectedfeatures.cpp

@@ -69,6 +69,8 @@ QgsSaveSelectedFeatures *QgsSaveSelectedFeatures::createInstance() const
 QVariantMap QgsSaveSelectedFeatures::processAlgorithm( const QVariantMap &parameters, QgsProcessingContext &context, QgsProcessingFeedback *feedback )
 {
   QgsVectorLayer *selectLayer = parameterAsVectorLayer( parameters, QStringLiteral( "INPUT" ), context );
+  if ( !selectLayer )
+    throw QgsProcessingException( invalidSourceError( parameters, QStringLiteral( "INPUT" ) ) );
 
   QString dest;
   std::unique_ptr< QgsFeatureSink > sink( parameterAsSink( parameters, QStringLiteral( "OUTPUT" ), context, dest, selectLayer->fields(), selectLayer->wkbType(), selectLayer->sourceCrs() ) );