For js code like:
with({}) { with({}) { with({}) { import x.x; }  }  }

the import statement can cause an exception, the import-exception is generated (but not fired) before it executes the other code.
The With-statement has 2 operations to push and pop the new scope it should be used with.
As the pre-generated Exception is already present, PushScope checks that and does not Push a new Scope.
But PopScope does not check that, and tries to pop, which leads us to a crash.
The Scope should be cleared by the Exceptionhandler on exception case, and PopScope should do nothing.

NOTE: I must admit I am unsure if this is the best solution, a review by a experienced kjs developer would be super helpful

Fixes the crash cases in the bugreport:

{with({}) { import window.x; } M:do {with(NaN = y)NaN = 1.3; } while(0); }
try { with({}) /*TODE2*/if(window) { if (V) {continue ;; }} else import set.x; } finally { x.__proto__ = x; }
try { with({}) { import x.*; }  } finally { return (x); }
with({}) { with({}) { with({}) { import x.x; }  }  }


and still keeps normal cases working like for example:
with({a:2}) { print(a); }
with(Math) { a= PI *2; print(a); }