Add spaces around concat operator

[hazzik]

Some dialects (DB2 for example) are confused by the concat operator without spaces. So let's just tweak it.

I did consider overriding only DB2Dialect but I think it is more beneficial if applied to all dialects.

[fredericDelaporte]

Isn't that more a bug fix than an improvement? I tend to think that

Some dialects (DB2 for example) are confused by the concat operator without spaces

means these dialects yield wrong results in such case or fail to execute the query.

This PR could also have removed the now redundant identical fix in HanaDialectBase.

[hazzik]

This PR could also have removed the now redundant identical fix in HanaDialectBase.

It is commented out there

Isn't that more a bug fix than an improvement?

Maybe... I’ll reclassify

[bahusoid]

It is commented out there

Nope:

nhibernate-core/src/NHibernate/Dialect/HanaDialectBase.cs

Line 457 in 14e2d87

RegisterFunction("concat", new VarArgsSQLFunction("(", " || ", ")"));

[hazzik]

Nope

Ok, I was thinking about some other dialect.

[fredericDelaporte]

Yes another dialect has it commented out, with a bunch of other registrations. (Code commented out should be removed, there is no point in keeping it in most case. But that was not the subject of this PR of course.)