[BUG] Edge case for preview image alignment

[Karthik Chikmagalur <karthikchikmagalur@gmail.com>]

Currently the value of `org-image-align' or of the `:align' attr_*
keyword is respected when previewing images in the following two
situations:

1. Image link in its own paragraph:

#+attr_org: :align center
[[file:/path/to/image.png]]

2. Image link at the end of a paragraph, on its own line:

Some text in a paragraph
#+attr_org: :align center
[[file:/path/to/image.png]]

OR

Some text in a paragraph
[[file:/path/to/image.png]]

But it is ignored when the 

3. image link is on its own line "inside" a paragraph:

Some text in a paragraph
#+attr_org: :align center
[[file:/path/to/image.png]]
followed by more text in the paragraph.

OR

Some text in a paragraph
[[file:/path/to/image.png]]
followed by more text in the paragraph.

-------

In contrast, the value of `org-image-max-width',
`org-image-actual-width' (and the attr_* :width attribute) are respected
in all three cases.

Should we support image alignment in case 3?

The only situation in which I can see this being undesirable is when you
have hard-wrapped/filled lines and the image link coincidentally ends up
on its own line.  In this case it doesn't make sense for the image
preview to respect `org-image-align'.  There might be other syntactical
reasons why supporting case 3 doesn't make sense, so I am asking here.

Karthik