Org reader: Allow image links with non-image targets

Org-Mode's own html exporter converts the following org link:

  [[http://example.com][https://www.haskell.org/static/img/logo.png]]

to

  <a href="http://example.com">
  <img src="https://www.haskell.org/static/img/logo.png" alt="logo.png" />
  </a>

but pandoc generates:

  <a href="http://example.com">
  <a href="https://www.haskell.org/static/img/logo.png" class="uri">
   https://www.haskell.org/static/img/logo.png
  </a>
  </a>

which is useless. With this patch, it generates:

  <a href="http://example.com">
  <img src="https://www.haskell.org/static/img/logo.png" alt="" />
  </a>

src/Text/Pandoc/Readers/Org.hs

@@ -1106,7 +1106,7 @@ explicitOrImageLink = try $ do
   char ']'
   return $ do
     src <- srcF
-    if isImageFilename src && isImageFilename title
+    if isImageFilename title
       then pure $ B.link src "" $ B.image title mempty mempty
       else linkToInlinesF src =<< title'