Fixed Emacs scala-mode indent (nil bug)

Currently, the Emacs scala-mode tool has bugs on my Emacs 23.3 in Ubuntu 12.04. I am using Evil, the Vi layer on top of Emacs, but the bug happens even in normal Emacs mode. For me, this code bugs out:

~~~{scala}
object Main {
  def fibs(x : Int) = {
    stuff
  }
}
~~~

On the bracket closing ``fibs``, if I type a newline, it would not indent and throw a ``(wrong-type-argument number-or-marker-p nil)`` error. Strangely, though, if I simply add a newline at the beginning of the entire file, there's no bug at all.

I went through the backtrace and found that it's the ``(char-before)`` at line 164 in scala-lambda-p in scala-mode-indent.el that was the problem. ``(char-before)`` returns nil if the pointer is out of range. I'm not sure why this would happen, but I've made a simple fix and it seems to work for me. Simply replace ``(char-before)`` with ``(preceding-char)`` on both lines 164 and 165. Someone should double-check that the bug occurs for them too and that the solution doesn't change anything, but otherwise this is an easy fix.