Fix performance problem from throwing/catching lots of exceptions

[jimrandomh]

runGetter is an inner-loop function that gets called every time anything is imported, and it showed up as a hotspot (~150ms) in my browser Javascript profiler results. Turns out, getter is sometimes null, which means that the small try/catch block here generates and consumes a null-reference exception. This is slow, much slower than handling the null case directly. Doing this reduces the time spent in this function to a much more reasonable ~30ms.

[crapthings]

same here

benjamn/install#60

we can even rewrite forEach to for loop

[benjamn]

Great idea—thanks @jimrandomh!