[mssql] Add workaround for incorrect geometry system type returned by sp_describe_first_result_set

Some (versions?) (setups?) of SQL server incorrectly report that
the system type for a geometry columns is "image" in their
sp_describe_first_result_set results.

Let's just automatically override this and set it back to "geometry"
if we know that the column is actually the geometry column.

Fixes broken query layers on these databases

Author: nyalldawson

src/providers/mssql/qgsmssqldatabase.cpp

@@ -403,6 +403,14 @@ bool QgsMssqlDatabase::loadQueryFields( FieldDetails &details, const QString &qu
     {
       details.geometryColumnName = name;
       details.geometryColumnType = systemTypeName;
+
+      // some versions/setups of SQL Server incorrectly report geometry columns as 'image' types in sp_describe_first_result_set results!
+      // let's just fix that up here...
+      if ( details.geometryColumnType == QLatin1String( "image" ) )
+      {
+        details.geometryColumnType = QStringLiteral( "geometry" );
+      }
+
       details.isGeography = systemTypeName == QLatin1String( "geography" );
     }
     else