Change empty-match exit from break 2 to break and add regression test (#46)

The break 2 was harder to reason about and could incorrectly abort parsing
when an empty match occurred mid-buffer with more stream data available.
With break (single), the iterator loads the next chunk, which can resolve
the empty match into a positive-length one (e.g. when a fixed-width
alternative needs more characters than remain in the current buffer).

Author: JanTvrdik

src/PatternIterator.php

@@ -82,7 +82,7 @@ public function getIterator(): Iterator
 				}
 
 				if (strlen($matches[0]) === 0) {
-					break 2;
+					break;
 				}
 
 				yield $matches;

tests/cases/PatternIteratorTest.phpt

@@ -524,6 +524,20 @@ class PatternIteratorTest extends TestCase
 	}
 
 
+	public function testZeroLengthMatchMidBufferLoadsMoreData(): void
+	{
+		// Pattern matches exactly 3 chars, or empty. When only 1 char remains in the
+		// buffer but the stream has more data, the empty match mid-buffer must not abort;
+		// loading the next chunk makes the 3-char alternative succeed.
+		$iter = new PatternIterator($this->stream('abXY', 'Zmore'), '~.{3}|~A');
+		$results = $this->collect($iter);
+		Assert::count(3, $results);
+		Assert::same('abX', $results[0][0]);
+		Assert::same('YZm', $results[1][0]);
+		Assert::same('ore', $results[2][0]);
+	}
+
+
 	public function testZeroLengthMatchAcrossChunks(): void
 	{
 		$pattern = '~\s*(?:(?<query>[^;]+);|\z)~As';