ERS: avoid 'Attempt at recursively opening ERS dataset' when the .ers…

… file references a .ecw (fixes OSGeo#9352)

The issue was no longer reproducible in master/3.9dev due to the
https://gdal.org/development/rfc/rfc96_deferred_plugin_loading.html
change, but was still somehow latent. This commit fixes the issue in the
3.8 branch

autotest/gdrivers/data/ers/references_ecw.ers

@@ -0,0 +1,14 @@
+DatasetHeader Begin
+	Version		= "6.2"
+	Name		= "references_ecw.ers"
+	DataFile	= "references_ecw.ecw"
+	DataSetType	= Translated
+	DataType	= Raster
+	ByteOrder	= LSBFirst
+	RasterInfo Begin
+		CellType	= Unsigned8BitInteger
+		NrOfLines	= 512
+		NrOfCellsPerLine	= 519
+		NrOfBands	= 1
+	RasterInfo End
+DatasetHeader End

autotest/gdrivers/ers.py

@@ -319,6 +319,16 @@ def test_ers_recursive_opening():
         ds.GetFileList()
 
 
+###############################################################################
+# Test fix for https://github.com/OSGeo/gdal/issues/9352
+
+
+@pytest.mark.require_driver("ECW")
+def test_ers_open_data_file_ecw():
+
+    assert gdal.Open("data/ers/references_ecw.ers")
+
+
 ###############################################################################
 # Cleanup
 

frmts/ers/ersdataset.cpp

@@ -881,17 +881,18 @@ int ERSProxyRasterBand::GetOverviewCount()
 GDALDataset *ERSDataset::Open(GDALOpenInfo *poOpenInfo)
 
 {
+    if (!Identify(poOpenInfo) || poOpenInfo->fpL == nullptr)
+        return nullptr;
+
+    int &nRecLevel = GetRecLevel();
     // cppcheck-suppress knownConditionTrueFalse
-    if (GetRecLevel())
+    if (nRecLevel)
     {
         CPLError(CE_Failure, CPLE_AppDefined,
                  "Attempt at recursively opening ERS dataset");
         return nullptr;
     }
 
-    if (!Identify(poOpenInfo) || poOpenInfo->fpL == nullptr)
-        return nullptr;
-
     /* -------------------------------------------------------------------- */
     /*      Ingest the file as a tree of header nodes.                      */
     /* -------------------------------------------------------------------- */
@@ -1020,7 +1021,6 @@ GDALDataset *ERSDataset::Open(GDALOpenInfo *poOpenInfo)
     /* -------------------------------------------------------------------- */
     if (EQUAL(poHeader->Find("DataSetType", ""), "Translated"))
     {
-        int &nRecLevel = GetRecLevel();
         nRecLevel++;
         poDS->poDepFile = GDALDataset::FromHandle(
             GDALOpen(osDataFilePath, poOpenInfo->eAccess));