ScriptForge (SF_Dataset) fix GetRows() in chunks

Two bugs are fixed with this commit:

1. when rows in a dataset are read in chunks,
   one record is skipped errorneously between
   every two successive chunks.

2. In updatable datasets, the updatable fields
   need to be identified. This is done at
   dataset creation.
   Before: the IsDefinitelyWritable criterion was
           used, valid for Firebird, not for HSQL
   After:  the IsWritable criterion is used,
           valid for both.

The correction in Basic is valid as well for Python.
Documentation is unchanged.

Change-Id: I990c02aaa8a93123a7e669b1294605fa19780167
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/160163
Reviewed-by: Jean-Pierre Ledure <jp@ledure.be>
Tested-by: Jenkins

wizards/source/sfdatabases/SF_Database.xba

@@ -28,7 +28,7 @@ Option Explicit
 '''		Transaction handling
 '''			Changes to data remain reversible until the moment the running script instructs the database to commit them.
 '''			The implicit (default) behaviour is that commit takes place after the execution of every single SQL statement.
-'''			The choice can be made (SetTranactionMode()) to take commitments manually.
+'''			The choice can be made (SetTransactionMode()) to take commitments manually.
 '''			The Commit() and Rollback() statements delimit transactions.
 '''
 '''		Service invocation and usage:

wizards/source/sfdatabases/SF_Dataset.xba

@@ -585,6 +585,7 @@ Check:
 		If Not ScriptForge.SF_Utils._Validate(Header, "Header", ScriptForge.V_BOOLEAN) Then GoTo Finally
 		If Not ScriptForge.SF_Utils._Validate(MaxRows, "MaxRows", ScriptForge.V_NUMERIC) Then GoTo Finally
 	End If
+	If MaxRows < 0 Then MaxRows = 1
 
 Try:
 	With _RowSet
@@ -608,7 +609,7 @@ Try:
 			End If
 
 			'	Load data
-			Do While bRead And (MaxRows = 0 Or lRows < MaxRows - 1)
+			Do While bRead
 				lRows = lRows + 1
 				If lRows = 0 Then
 					ReDim vResult(0 To lRows, 0 To lCols)
@@ -618,7 +619,7 @@ Try:
 				For i = 0 To lCols
 					vResult(lRows, i) = _ParentDatabase._GetColumnValue(_RowSet, i + 1)
 				Next i
-				bRead = .next()
+				If MaxRows = 0 Or lRows < MaxRows - 1 Then bRead = .next() Else bRead = False
 			Loop
 
 		Else
@@ -1343,7 +1344,7 @@ Try:
 					'	Field names
 					sFields = sFields & "," & .Name
 					'	Updatable field names
-					If Not _ReadOnly And .isDefinitelyWritable And Not .IsAutoIncrement Then sUpdatableFields = sUpdatableFields & "," & .Name
+					If Not _ReadOnly And .IsWritable And Not .IsAutoIncrement Then sUpdatableFields = sUpdatableFields & "," & .Name
 					'	Default values
 					_DefaultValues(i) = _ConvertDefaultValue(oColumn)
 					'	AutoValue