Don't fold postscriptum standalone comment into last statement

This happened when the last statement was a simple statement.

Fixes #18
Fixes #28

README.md

@@ -272,6 +272,11 @@ More details can be found in [CONTRIBUTING](CONTRIBUTING.md).
 * if top level functions were separated by a comment, don't put four
   empty lines after the upper function
 
+* fixed unstable formatting of newlines with imports
+
+* fixed unintentional folding of post scriptum standalone comments
+  into last statement if it was a simple statement (#18, #28)
+
 * fixed missing space in numpy-style array indexing (#33)
 
 * fixed spurious space after star-based unary expressions (#31)

black.py

@@ -1115,7 +1115,7 @@ def generate_comments(leaf: Leaf) -> Iterator[Leaf]:
     if content and (content[0] not in {' ', '!', '#'}):
         content = ' ' + content
     is_standalone_comment = (
-        '\n' in before_comment or '\n' in content or leaf.type == token.DEDENT
+        '\n' in before_comment or '\n' in content or leaf.type == token.ENDMARKER
     )
     if not is_standalone_comment:
         # simple trailing comment

tests/expression.py

@@ -124,6 +124,9 @@ async def f():
     signal.getsignal(signal.SIGINT) != signal.default_int_handler
 ):
     return True
+last_call()
+# standalone comment at ENDMARKER
+
 
 # output
 
@@ -275,3 +278,6 @@ async def f():
     or signal.getsignal(signal.SIGINT) != signal.default_int_handler
 ):
     return True
+
+last_call()
+# standalone comment at ENDMARKER