py/vm: Fix popping of exception block in UNWIND_JUMP opcode.

Fixes issue #1812.

py/vm.c

@@ -674,7 +674,7 @@ unwind_jump:;
                             exc_sp--; // pop exception handler
                             goto dispatch_loop; // run the exception handler
                         }
-                        exc_sp--;
+                        POP_EXC_BLOCK();
                     }
                     ip = (const byte*)MP_OBJ_TO_PTR(POP()); // pop destination ip for jump
                     if (unum != 0) {

tests/basics/try_continue.py

+# test continue within exception handler
+
+def f():
+    lst = [1, 2, 3]
+    for x in lst:
+        print('a', x)
+        try:
+            if x == 2:
+                raise Exception
+        except Exception:
+            continue
+        print('b', x)
+f()