fix intersection with zero area rectangles

[davidmoten]

See discussion in #91.

I've started with rectangleIntersectsLine. Might have to check rectangle intersects rectangle case too.

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@6798826). Click here to learn what that means.
The diff coverage is 100%.

@@            Coverage Diff            @@
##             master      #92   +/-   ##
=========================================
  Coverage          ?   75.68%           
  Complexity        ?      833           
=========================================
  Files             ?       72           
  Lines             ?     2344           
  Branches          ?      316           
=========================================
  Hits              ?     1774           
  Misses            ?      478           
  Partials          ?       92

Impacted Files	Coverage Δ	Complexity Δ
...ithub/davidmoten/rtree/internal/RectangleUtil.java	59.61% <100%> (ø)	21 <3> (?)

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[davidmoten]

Build is actually fine, will sort travis stuff out later.

I don't think further action is required on this PR so I'm going to merge.