make quoted capture less greedy when we have unambiguous separator

In [#60][], GitHub user @robcowart reports
that in some scenarios we can fail to split on match of `field_split_pattern`.

The example given is a partially-quoted value, with additional bytes between
it and the unambiguous separator, followed by another key and quoted value.

Since the quoted value isn't immediately followed by a field splitter, our
semi-greedy quoted-value capture was too greedy, continuing to consume until
it found a close-quote that would be followed by either a field-split or EOF.

Here, we become much less greedy, capturing any sequence of characters that
is _not_ the close-quote character.

[#60]: #60

Fixes #62

lib/logstash/filters/kv.rb

@@ -422,8 +422,8 @@ def quoted_capture(quote_sequence, close_quote_sequence=quote_sequence)
     open_pattern = /#{Regexp.quote(quote_sequence)}/
     close_pattern = /#{Regexp.quote(close_quote_sequence)}/
 
-    # matches a sequence of zero or more characters that is followed by the `close_quote_sequence`
-    quoted_value_pattern = /(?:.)*?(?=#{Regexp.quote(close_quote_sequence)})/
+    # matches a sequence of zero or more characters are _not_ the `close_quote_sequence`
+    quoted_value_pattern = /[^#{Regexp.quote(close_quote_sequence)}]*/
 
     /#{open_pattern}(#{quoted_value_pattern})#{close_pattern}/
   end

spec/filters/kv_spec.rb

@@ -833,6 +833,40 @@
     it_behaves_like "parsing all fields and values"
   end
 
+  context 'multi-char field split pattern with value that begins quoted and contains more unquoted' do
+    let(:message) { 'foo=bar!!!!!baz="quoted stuff" and more unquoted!!!!!msg="fully-quoted with a part! of the separator"!!!!!blip="this!!!!!is it"!!!!!empty=""!!!!!non-empty="foo"' }
+    let(:options) {
+      {
+          "field_split_pattern" => "!!!!!"
+      }
+    }
+    it 'gets the right bits' do
+      subject.filter(event)
+      expect(event.get("foo")).to eq('bar')
+      expect(event.get("baz")).to eq('"quoted stuff" and more unquoted')
+      expect(event.get("msg")).to eq('fully-quoted with a part! of the separator')
+      expect(event.get("blip")).to eq('this!!!!!is it')
+      expect(event.get("empty")).to be_nil
+      expect(event.get("non-empty")).to eq('foo')
+    end
+  end
+
+  context 'standard field split pattern with value that begins quoted and contains more unquoted' do
+    let(:message) { 'foo=bar baz="quoted stuff" and more unquoted msg="some fully-quoted message " empty="" non-empty="foo"' }
+    let(:options) {
+      {
+      }
+    }
+    it 'gets the right bits' do
+      subject.filter(event)
+      expect(event.get("foo")).to eq('bar')
+      expect(event.get("baz")).to eq('quoted stuff') # NOTE: outside the quotes is truncated because field split pattern wins.
+      expect(event.get("msg")).to eq('some fully-quoted message ')
+      expect(event.get("empty")).to be_nil
+      expect(event.get("non-empty")).to eq('foo')
+    end
+  end
+
   context "field and value split multi" do
     let(:message) { "hello::world__foo::bar__baz::fizz__doublequoted::\"hello world\"__singlequoted::'hello world'__bracketsone::(hello world)__bracketstwo::[hello world]__bracketsthree::<hello world>" }
     let(:options) {