[GRASS] coverity fixes

src/providers/grass/qgsgrass.cpp

@@ -593,7 +593,11 @@ void QgsGrass::setLocation( QString gisdbase, QString location )
 void QgsGrass::setMapset( QString gisdbase, QString location, QString mapset )
 {
   QgsDebugMsg( QString( "gisdbase = %1 location = %2 mapset = %3" ).arg( gisdbase, location, mapset ) );
-  init();
+  if ( !init() )
+  {
+    QgsDebugMsg( QgsGrass::initError() );
+    return;
+  }
 
   // Set principal GRASS variables (in memory)
 #ifdef Q_OS_WIN

tests/src/providers/grass/testqgsgrassprovider.cpp

@@ -1061,6 +1061,13 @@ void TestQgsGrassProvider::edit()
 
         expectedLayer->startEditing();
       }
+
+      if ( !grassLayer || !grassProvider || !expectedLayer )
+      {
+        reportRow( "grassLayer, grassProvider or expectedLayer is null" );
+        commandOk = false;
+        break;
+      }
       else if ( command.command == TestQgsGrassCommand::CommitChanges )
       {
         grassLayer->commitChanges();