Use faster static QFileInfo::exists instead of constructing QFileInfo

Thanks to Clazy

Author: nyalldawson

src/app/dwg/qgsdwgimportdialog.cpp

@@ -151,7 +151,7 @@ void QgsDwgImportDialog::on_leLayerGroup_textChanged( const QString &text )
 
 void QgsDwgImportDialog::on_pbLoadDatabase_clicked()
 {
-  if ( !QFileInfo( leDatabase->text() ).exists() )
+  if ( !QFileInfo::exists( leDatabase->text() ) )
     return;
 
   CursorOverride waitCursor;

src/app/dwg/qgsdwgimporter.cpp

@@ -195,7 +195,7 @@ bool QgsDwgImporter::import( const QString &drawing, QString &error, bool doExpa
     return false;
   }
 
-  if ( QFileInfo( mDatabase ).exists() )
+  if ( QFileInfo::exists( mDatabase ) )
   {
     mDs = OGROpen( mDatabase.toUtf8().constData(), true, nullptr );
     if ( !mDs )