Fixed typed-array ctor when source array is changed while iterating.

Fixed typed-array ctor when source array is changed while iterating.

Previously, the function used optimization for ordinary arrays with no
gaps (so called fast arrays).  For a fast array code took elements
directly from internal flat C array. The direct pointer may become
invalid as side-effect of custom valueOf() method for an element.

The fix is to eliminate the micro-optimization which uses direct
pointers.

The problem is similar to the 9578cc729205 (0.7.2) commit.

This closes #523 issue on Github.