[processing] Try directly interpreting string as CRS first

...before falling back to alternatives like treating it as a map
layer

Fixes #57494

src/core/processing/qgsprocessingparameters.cpp

@@ -3114,6 +3114,13 @@ QString QgsProcessingParameterCrs::valueAsPythonString( const QVariant &value, Q
 
 QString QgsProcessingParameterCrs::valueAsString( const QVariant &value, QgsProcessingContext &context, bool &ok ) const
 {
+  if ( value.type() == QVariant::String )
+  {
+    const QgsCoordinateReferenceSystem crs( value.toString() );
+    if ( crs.isValid() )
+      return value.toString();
+  }
+
   return valueAsStringPrivate( value, context, ok, ValueAsStringFlag::AllowMapLayerValues );
 }
 

src/core/processing/qgsprocessingutils.cpp

@@ -675,14 +675,17 @@ QgsCoordinateReferenceSystem QgsProcessingUtils::variantToCrs( const QVariant &v
   if ( context.project() && crsText.compare( QLatin1String( "ProjectCrs" ), Qt::CaseInsensitive ) == 0 )
     return context.project()->crs();
 
+  // else CRS from string
+  const QgsCoordinateReferenceSystem crs( crsText );
+  if ( crs.isValid() )
+    return crs;
+
   // maybe a map layer reference
   if ( QgsMapLayer *layer = QgsProcessingUtils::mapLayerFromString( crsText, context ) )
     return layer->crs();
 
-  // else CRS from string
-  QgsCoordinateReferenceSystem crs;
-  crs.createFromString( crsText );
-  return crs;
+  // no luck!
+  return QgsCoordinateReferenceSystem();
 }
 
 bool QgsProcessingUtils::canUseLayer( const QgsMeshLayer *layer )