VS: Fix .vcxproj indentation

In commit v3.8.0-rc1~87^2~1 (VS: added support for C#, 2017-01-09) we
removed what looked like a no-op streaming operation but in fact it
is responsible for applying indentation.  Restore the line.

Source/cmVisualStudio10TargetGenerator.cxx

@@ -130,6 +130,7 @@ void cmVisualStudio10TargetGenerator::WritePlatformConfigTag(
   }
   stream->fill(' ');
   stream->width(indentLevel * 2);
+  (*stream) << ""; // applies indentation
   (*stream) << "<" << tag << " Condition=\"";
   (*stream) << "'$(Configuration)|$(Platform)'=='";
   (*stream) << config << "|" << this->Platform;