fixes #17170 (#17171)

tests/arc/torcmisc.nim

@@ -0,0 +1,34 @@
+discard """
+  output: '''success'''
+  cmd: "nim c --gc:orc -d:release $file"
+"""
+
+# bug #17170
+
+when true:
+  import asyncdispatch
+
+  type
+    Flags = ref object
+      returnedEof, reading: bool
+
+  proc dummy(): Future[string] {.async.} =
+    result = "foobar"
+
+  proc hello(s: Flags) {.async.} =
+    let buf =
+      try:
+        await dummy()
+      except CatchableError as exc:
+        # When an exception happens here, the Bufferstream is effectively
+        # broken and no more reads will be valid - for now, return EOF if it's
+        # called again, though this is not completely true - EOF represents an
+        # "orderly" shutdown and that's not what happened here..
+        s.returnedEof = true
+        raise exc
+      finally:
+        s.reading = false
+
+  waitFor hello(Flags())
+  echo "success"
+