fix(39): incorrect parsing and panic involving consecutive @if expressions and interpolation blocks

[ninoDeme]

fixes #39
Dirty fix to resolve the problem.

The change in scanner.c should fix the crash when the syntax tree is invalid and i wasn't able to find a way to fix the precedence rules of the @if statement without breaking the @else and @else if statements, so i just made the @else if and @else statements separate from the @if statement

[Ryntak94]

Out of curiosity, do you think this fix will address my issue? :)
#41

[dlvandenberg]

@ninoDeme Thanks for this. I was working on this before my holidays. I did miss the bug in the scanner. I've created a new PR #43

[dlvandenberg]

@Ryntak94 No that's a separate issue.