[delimitertext] fix watcher check ignored and harmful watcher created for iterator

(fixes #15558)

(cherry-picked from b3e3108)

Author: nirvn

src/providers/delimitedtext/qgsdelimitedtextfeatureiterator.cpp

@@ -501,8 +501,16 @@ QgsDelimitedTextFeatureSource::QgsDelimitedTextFeatureSource( const QgsDelimited
     , mXyDms( p->mXyDms )
     , attributeColumns( p->attributeColumns )
 {
+  QUrl url = p->mFile->url();
+
+  // make sure watcher not created when using iterator (e.g. for rendering, see issue #15558)
+  if ( url.hasQueryItem( "watchFile" ) )
+  {
+    url.removeQueryItem( "watchFile" );
+  }
+
   mFile = new QgsDelimitedTextFile();
-  mFile->setFromUrl( p->mFile->url() );
+  mFile->setFromUrl( url );
 
   mExpressionContext << QgsExpressionContextUtils::globalScope()
   << QgsExpressionContextUtils::projectScope();

src/providers/delimitedtext/qgsdelimitedtextfile.cpp

@@ -35,7 +35,7 @@ QgsDelimitedTextFile::QgsDelimitedTextFile( const QString& url ) :
     mEncoding( "UTF-8" ),
     mFile( nullptr ),
     mStream( nullptr ),
-    mUseWatcher( true ),
+    mUseWatcher( false ),
     mWatcher( nullptr ),
     mDefinitionValid( false ),
     mUseHeader( true ),
@@ -158,9 +158,9 @@ bool QgsDelimitedTextFile::setFromUrl( const QUrl &url )
   }
 
   //
-  if ( url.hasQueryItem( "useWatcher" ) )
+  if ( url.hasQueryItem( "watchFile" ) )
   {
-    mUseWatcher = ! url.queryItemValue( "useWatcher" ).toUpper().startsWith( 'N' );
+    mUseWatcher = url.queryItemValue( "watchFile" ).toUpper().startsWith( 'Y' );
   }
 
   // The default type is csv, to be consistent with the
@@ -269,9 +269,9 @@ QUrl QgsDelimitedTextFile::url()
     url.addQueryItem( "encoding", mEncoding );
   }
 
-  if ( !mUseWatcher )
+  if ( mUseWatcher )
   {
-    url.addQueryItem( "useWatcher", "no" );
+    url.addQueryItem( "watchFile", "yes" );
   }
 
   url.addQueryItem( "type", type() );