minirst: do not add a 2nd empty paragraph

This does not add a separating block after a separated note directive.

.. note::

    text

is formatted to

Note:
    text

mercurial/minirst.py

@@ -381,6 +381,9 b' def addmargins(blocks):'
         if (blocks[i]['type'] == blocks[i - 1]['type'] and
             blocks[i]['type'] in ('bullet', 'option', 'field')):
             i += 1
+        elif not blocks[i - 1]['lines']:
+            # no lines in previous block, do not seperate
+            i += 1
         else:
             blocks.insert(i, dict(lines=[''], indent=0, type='margin'))
             i += 2