njs_vm_run() is rectified.

njs_vm_run() is rectified.

Previously, both njs_vm_call() and njs_vm_run() can be used to run njs
code. njs_vm_call() was used to invoke a single function, while
njs_vm_run() was used to run global code as well to process the events.

At first invocation njs_vm_run() executed global code, all the next
invocations it processed pending events.

The solution is splitting njs_vm_run() into two functions. One for
events processing and another for running the global code.