Fix nested finally handling in closureiters [backport] (#19933)

* Fix nested finally handling in closureiters

* Fix CI

* review comment

* third time the charm

* Update compiler/closureiters.nim

Co-authored-by: Dominik Picheta <dominikpicheta@googlemail.com>

Co-authored-by: Dominik Picheta <dominikpicheta@googlemail.com>

tests/iter/titer_issues.nim

@@ -30,6 +30,14 @@ end
 @[1, 2]
 @[1, 2, 3]
 1
+nested finally
+outer finally
+nested finally
+outer finally
+nested finally
+outer finally
+nested finally
+outer finally
 '''
 """
 
@@ -287,3 +295,70 @@ block:
 
   for i in a(5):
     echo i
+
+block:
+  # bug #19911 (return in nested try)
+
+  # try yield -> try
+  iterator p1: int {.closure.} =
+    try:
+      yield 0
+      try:
+        return
+      finally:
+        echo "nested finally"
+      echo "shouldn't run"
+    finally:
+      echo "outer finally"
+    echo "shouldn't run"
+
+  for _ in p1():
+    discard
+
+  # try -> try yield
+  iterator p2: int {.closure.} =
+    try:
+      try:
+        yield 0
+        return
+      finally:
+        echo "nested finally"
+      echo "shouldn't run"
+    finally:
+      echo "outer finally"
+    echo "shouldn't run"
+
+  for _ in p2():
+    discard
+
+  # try yield -> try yield
+  iterator p3: int {.closure.} =
+    try:
+      yield 0
+      try:
+        yield 0
+        return
+      finally:
+        echo "nested finally"
+      echo "shouldn't run"
+    finally:
+      echo "outer finally"
+    echo "shouldn't run"
+
+  for _ in p3():
+    discard
+
+  # try -> try
+  iterator p4: int {.closure.} =
+    try:
+      try:
+        return
+      finally:
+        echo "nested finally"
+      echo "shouldn't run"
+    finally:
+      echo "outer finally"
+    echo "shouldn't run"
+
+  for _ in p4():
+    discard