MIraMonRaster: fixing fuzzer Issue 443651667

A band name may be empty only if it is the only band present in the REL file. Otherwise, inferring the band name from the REL filename is considered an error.  Consequently, for a REL file containing exactly one band, if the band name is empty, it shall be inferred from the REL filename.
Example: REL: testI.rel  -->  IMG: test.img

Author: AbelPau

frmts/miramon/miramon_band.cpp

@@ -27,20 +27,33 @@ MMRBand::MMRBand(MMRRel &fRel, const CPLString &osBandSectionIn)
       m_osBandSection(osBandSectionIn)
 
 {
-    // Getting band and band file name from metadata
+    // Getting band and band file name from metadata.
     if (!m_pfRel->GetMetadataValue(SECTION_ATTRIBUTE_DATA, osBandSectionIn,
                                    KEY_NomFitxer, m_osRawBandFileName) ||
         m_osRawBandFileName.empty())
     {
-        m_osBandFileName =
-            m_pfRel->MMRGetFileNameFromRelName(m_pfRel->GetRELName());
+        // A band name may be empty only if it is the only band present
+        // in the REL file. Otherwise, inferring the band name from the
+        // REL filename is considered an error.
+        // Consequently, for a REL file containing exactly one band, if
+        // the band name is empty, it shall be inferred from the REL
+        // filename.
+        // Example: REL: testI.rel  -->  IMG: test.img
+        if (m_pfRel->GetNBands() >= 1)
+            m_osBandFileName = "";
+        else
+        {
+            m_osBandFileName =
+                m_pfRel->MMRGetFileNameFromRelName(m_pfRel->GetRELName());
+        }
+
         if (m_osBandFileName.empty())
         {
             m_nWidth = 0;
             m_nHeight = 0;
             CPLError(CE_Failure, CPLE_AssertionFailed,
                      "The REL file '%s' contains a documented \
-                band with no explicit name. Section [%s] or [%s:%s].",
+                band with no explicit or wrong name. Section [%s] or [%s:%s].",
                      m_pfRel->GetRELNameChar(), SECTION_ATTRIBUTE_DATA,
                      SECTION_ATTRIBUTE_DATA, m_osBandSection.c_str());
             return;