Coverity null deference fixes

Author: nyalldawson

src/app/qgsmaptooladdcircularstring.cpp

@@ -79,7 +79,7 @@ void QgsMapToolAddCircularString::keyPressEvent( QKeyEvent* e )
 
 void QgsMapToolAddCircularString::keyReleaseEvent( QKeyEvent* e )
 {
-  if ( e->isAutoRepeat() )
+  if ( e && e->isAutoRepeat() )
   {
     return;
   }

src/core/composer/qgsatlascomposition.cpp

@@ -838,7 +838,7 @@ QgsExpressionContext QgsAtlasComposition::createExpressionContext()
   expressionContext << new QgsExpressionContextScope( "Atlas" );
   if ( mCoverageLayer )
     expressionContext.lastScope()->setFields( mCoverageLayer->fields() );
-  if ( mComposition->atlasMode() != QgsComposition::AtlasOff )
+  if ( mComposition && mComposition->atlasMode() != QgsComposition::AtlasOff )
     expressionContext.lastScope()->setFeature( mCurrentFeature );
 
   return expressionContext;

src/core/composer/qgscomposerattributetable.cpp

@@ -396,7 +396,7 @@ bool QgsComposerAttributeTable::getFeatureAttributes( QList<QgsAttributeMap> &at
   if ( mComposerMap && mShowOnlyVisibleFeatures )
   {
     selectionRect = *mComposerMap->currentMapExtent();
-    if ( mVectorLayer && mComposition->mapSettings().hasCrsTransformEnabled() )
+    if ( mComposition->mapSettings().hasCrsTransformEnabled() )
     {
       //transform back to layer CRS
       QgsCoordinateTransform coordTransform( mVectorLayer->crs(), mComposition->mapSettings().destinationCrs() );

src/server/qgswmsserver.cpp

@@ -2687,11 +2687,8 @@ void QgsWMSServer::applyOpacities( const QStringList& layerList, QList< QPair< Q
       //modify symbols of current renderer
       QgsRenderContext context;
       context.expressionContext() << QgsExpressionContextUtils::globalScope()
-      << QgsExpressionContextUtils::projectScope();
-      if ( vl )
-      {
-        context.expressionContext() << QgsExpressionContextUtils::layerScope( vl );
-      }
+      << QgsExpressionContextUtils::projectScope()
+      << QgsExpressionContextUtils::layerScope( vl );
 
       QgsSymbolV2List symbolList = rendererV2->symbols( context );
       QgsSymbolV2List::iterator symbolIt = symbolList.begin();