fix:add,import,web: really avoid filenames ending with . on Windows [#1056]

On MS Windows, trying to add or import or web add to a file whose name
ends with a dot could cause data loss, so in 2019 I made this raise an
error instead (in Hledger.Read.ensureJournalFileExists).

But, the logic was backward, so it did not do the check on Windows.
Now it does.

Also I have removed mention of this from add's doc; currently it's
not documented anywhere. It's obscure, but maybe this is not ideal.

hledger-lib/Hledger/Read.hs

@@ -348,7 +348,7 @@ requireJournalFileExists f = do
 -- which could cause data loss (see 'isWindowsUnsafeDotPath').
 ensureJournalFileExists :: FilePath -> IO ()
 ensureJournalFileExists f = do
-  when (os/="mingw32" && isWindowsUnsafeDotPath f) $ do
+  when (os=="mingw32" && isWindowsUnsafeDotPath f) $ do
     hPutStr stderr $ "Part of file path \"" <> show f <> "\"\n ends with a dot, which is unsafe on Windows; please use a different path.\n"
     exitFailure
   exists <- doesFileExist f

hledger/Hledger/Cli/Commands/Add.md

@@ -67,7 +67,3 @@ and you have declared a default commodity with a `D` directive,
 you might expect `add` to add this symbol for you.
 It does not do this; we assume that if you are using a `D` directive
 you prefer not to see the commodity symbol repeated on amounts in the journal.
-
-On Microsoft Windows, the add command makes sure that no part of the
-file path ends with a period, as that would cause problems
-([#1056](https://github.com/simonmichael/hledger/issues/1056)).