fix(scala): parse guard in generator if there is a newline

[brandonspark]

Goes with #6033.

What: We currently fail to parse Scala programs which contain newlines before the guard of generator expressions.

Why: This breaks some use cases. For instance, we cannot parse:

for {
  x <- 3
  if b 
} yield 3

How: I just added a thing which, irregardless of if there is a newline or space, checks beyond it to see if the next token is an if. If so, then it enters the guard loop.

Test plan: make test

Security

• [x] Change has no security implications (otherwise, ping the security team)

[brandonspark]

Turns out the segfaults were because of an infinite loop. On another architecture, they seemed not to loop though. Kind of wild.

[aryx]

I'll try to look at the circleCI error tomorrow. I think I know why.