avoid running finish_task inside of throw_internal

if throw_internal is running from the segv_handler, there might not be enough stack to run arbitrary functions
this change, therefore, makes stack overflow in tasks more reliable

src/task.c

@@ -238,8 +238,16 @@ static void NOINLINE NORETURN start_task()
 {
     // this runs the first time we switch to a task
     jl_task_t *t = jl_current_task;
+    jl_value_t *res;
     throw_if_exception_set(t);
-    jl_value_t *res = jl_apply(t->start, NULL, 0);
+    JL_TRY {
+        res = jl_apply(t->start, NULL, 0);
+    }
+    JL_CATCH {
+        res = jl_exception_in_transit;
+        t->exception = res;
+        jl_gc_wb(t, res);
+    }
     finish_task(t, res);
     abort();
 }
@@ -668,17 +676,11 @@ void NORETURN throw_internal(jl_value_t *e)
         jl_longjmp(jl_current_task->eh->eh_ctx, 1);
     }
     else {
-        if (jl_current_task == jl_root_task) {
-            jl_printf(JL_STDERR, "fatal: error thrown and no exception handler available.\n");
-            jl_static_show(JL_STDERR, e);
-            jl_printf(JL_STDERR, "\n");
-            jlbacktrace();
-            jl_exit(1);
-        }
-        jl_current_task->exception = e;
-        jl_gc_wb(jl_current_task, e);
-        finish_task(jl_current_task, e);
-        assert(0);
+        jl_printf(JL_STDERR, "fatal: error thrown and no exception handler available.\n");
+        jl_static_show(JL_STDERR, e);
+        jl_printf(JL_STDERR, "\n");
+        jlbacktrace();
+        jl_exit(1);
     }
     assert(0);
 }