Fix snippet reader tab and indent handling

[Jotschi]

The PR addresses the following issues:

• The snippet reader did not correctly apply the indentation for snippet sources which were indented using tabs. The minIndent calculation only checked spaces.

Snippet Source:

[tab][tab]line

Old Behaviour

[tab][tab]line

New Behaviour:

line

• The snippet reader minIndent calculation was always 0 whenever the snippet contained empty newlines. Those empty lines will now correctly be handled.

Snippet Source:

[space][space]line1
[\n]
[space]line2

Old Behaviour

[space][space]line1
[\n]
[space]line2

New Behaviour:

line1
[\n]
[space]line2