Fix a few Coverity warnings.

eeschema/files-io.cpp

@@ -470,8 +470,10 @@ bool SCH_EDIT_FRAME::OpenProjectFiles( const std::vector<wxString>& aFileSet, in
                            "new file format cannot be opened with previous versions of KiCad." ) );
                 newFileFormatDlg.ShowCheckBox( _( "Do not show this dialog again." ) );
                 newFileFormatDlg.ShowModal();
-                cfg->m_Appearance.show_sexpr_file_convert_warning =
-                        !newFileFormatDlg.IsCheckBoxChecked();
+
+                if( cfg )
+                    cfg->m_Appearance.show_sexpr_file_convert_warning =
+                            !newFileFormatDlg.IsCheckBoxChecked();
             }
 
             // Allow the schematic to be saved to new file format without making any edits.

eeschema/sch_sexpr_plugin.cpp

@@ -471,6 +471,7 @@ SCH_SHEET* SCH_SEXPR_PLUGIN::Load( const wxString& aFileName, KIWAY* aKiway,
 
         // If we got here, the schematic loaded successfully.
         sheet = newSheet.release();
+        m_rootSheet = nullptr;         // Quiet Coverity warning.
     }
     else
     {

eeschema/tools/sch_editor_control.cpp

@@ -854,7 +854,7 @@ int SCH_EDITOR_CONTROL::UpdateNetHighlighting( const TOOL_EVENT& aEvent )
             {
                 SCH_CONNECTION* pin_conn = comp->GetConnectionForPin( pin, *g_CurrentSheet );
 
-                if( pin_conn && pin_conn->Name( false ) == selectedNetName )
+                if( comp && pin_conn && pin_conn->Name( false ) == selectedNetName )
                 {
                     comp->BrightenPin( pin );
                     redraw = true;

pcbnew/pcbnew_settings.cpp

@@ -46,6 +46,7 @@ const int pcbnewSchemaVersion = 0;
 PCBNEW_SETTINGS::PCBNEW_SETTINGS() : APP_SETTINGS_BASE( "pcbnew", pcbnewSchemaVersion ),
         m_Use45DegreeGraphicSegments( false ),
         m_FlipLeftRight( false ),
+        m_ShowPageLimits( true ),
         m_MagneticPads( MAGNETIC_OPTIONS::CAPTURE_CURSOR_IN_TRACK_TOOL ),
         m_MagneticTracks( MAGNETIC_OPTIONS::CAPTURE_CURSOR_IN_TRACK_TOOL ),
         m_MagneticGraphics( true ),