Dynamic columns in insert and update should handle the case of empty object/array

Consider this scenario:

const user = { name: 'Murray', age: 68 }
let columns = [];  // will be filled later 

// assume something went wrong and columns is still empty

await sql`
  insert into users ${
    sql(user, [])
  }
`

Or maybe this:

const user = {}; // will be filled later

// assume something went wrong and user is still empty

await sql`
  insert into users ${
    sql(user)
  }
`

We get this no-so-informative error: PostgresError: syntax error at or near "where".

Since dynamic columns can be, by definition, very dynamic, I think it would make sense to handle these special cases:

• the object with data (first argument) is "empty"
• the columns array (second argument) is empty

It would be a simple change in src/types.js, in the update and insert entries in the builders: https://github.com/porsager/postgres/blob/master/cjs/src/types.js#L164-L176

Before using the escapeIdentifier, it would be a matter of checking if the array is empty.

Read src/types.js, especially the update and insert builders, and reproduce the two examples with an empty object or columns array. Verify behavior for both empty-input cases so neither produces the reported uninformative PostgreSQL syntax error.